Does "holds Professorship" mean that he is a professor?

In the British education system, only very senior academic staff are called "professors", usually heads of departments. Some prestigious professor posts (professorships) are named, like the one mentioned.

Adjunct and associate professors are job titles from the (different) North American education system.

Cool.

Yes, in America professors seem to be little more than lecturers. The top man in a department might be called the Dean. Or is that the top man in the whole college?
Correct me if I'm wrong.
And the meaning of "college" is different in the two countries too. Likewise "school".

In the USA they would probably call it a "chair. This is an office or title named after someone they wanted to honor (Andreas Idreos in this case).

So, yeah, that's what it means. Another example: The guy who "holds the office of president" is, guess what? The president. And it wouldn't include the vice-president.

It is more difficult to describe the "American" system, because there isn't one. So, for example, the University of Toronto is made up of affiliated colleges, just as are universities in England (i'm not claiming expertise on the system in England, although i do know somewhat of the history). The terms university and college are often used interchangeably in the United States--although college is often the preferred term. A working class tough might sneer at someone who is better spoken than he is by calling that man a "college boy." Americans are more likely to say that someone is in college rather than to say that they are at university. I have developed the habit of referring to my education by saying university (and i did attend two institutions which are named universities), because online one meets so many native-speakers of English who are not from the United States, and it avoids confusion on the part of one's interlocutors. Informally, in the United States, collage is often used to describe a small institution of higher education, while university refers to larger schools, or state systems. For exaqmple, there are state universities in New York, referred to as "SUNY." The University of Stony Brook is often called SUNY Stony Brook. Illinois and California also have extensive university systems. I am most familiar with Illinois' system, having been employed at the University of Illinois at Urbana-Champaign and at Southern Illinois University at Carbondale. I was educated at Illinois State University and the University of Illinois, U-C. Both the U of I and Southern Illinois University have several campuses--but they are not affiliated colleges such as one sees with Oxford and Cambridge. Actually ISU is the oldest university in Illinois, established in 1857 as a normal college, normal in the French sense of a teacher training school, an école normale. It is the first or one of the first "land grant" universities in the United States--local Bloomington, Illinois businessman Jesse Fell granted land for the school. Fell became Lincoln's campaign manager in the 1860 elections. Naturally, a town grew up around the school, and was incorporated as Normal, Illinois--a name which afforded us much rather witless adolescent mirth. Land grant universities proliferated after the American civil war, and state universities dominate the higher educational system of the United States.

Harvard University is the oldest institution of higher education in the United Sates, founded in 1636 with a land grant from John Harvard and funding from the Great and General Court of the Massachusetts Bay Company. Harvard was a minister in Charlestown, Massachusetts, then opposite Boston on a spit of land running out into Massachusetts Bay, between the Charles River and the Mystic River. Alas, most of Massachusetts Bay has been drained and paved over. Just behind the town is Breed's Hill, where Colonel William Prescott of the Massachusetts militia built a redoubt overnight in June, 1775, which, had it been supplied with artillery (it wasn't) would have forced the Royal Navy to abandon Boston. Lord Howe sent troops across to Charlestown Neck (as it was called), who advanced on the redoubt three times, suffering terrible casualties. Prescott and his men were forced out when they ran out of shot. The British circulated atrocity stories in Europe after the battle because in the final assault, Prescott's men had run out of shot and were shoving stones, nails and glass from broken bottles down their muskets. Most of the American militia, numbering more than 10,000, took no part in the battle, milling around on Plowed Hill and Bunker Hill nearby, and hence the name of the battle. Major Pitcairn of the Royal Marines was fatally wounded in the battle--his brother had sighted an island in the Pacific which was named after him, but the position was laid down wrong on their charts. In 1789, Fletcher Christian, fleeing Tahiti in HMAV Bounty with those mutineers who wished to remain with him, found and landed at Pitcairn's Island, where some of his descendants live to this day. All of which is more American history than you ever wanted to read, if you're still reading.

I have not addressed the matter of professors because others have given you good answers. Most of this will be on the test.