I'm of a grandmotherly age but with Dagmaraka on this unless you get other signals - but then I was informal the few times I lectured, myself.
Many professors don't need to speak from "on high" in order to command respect, and others prefer formality for... form's sake, with good arguments towards that.
I did have a long time friend that even demanded restaurants call him "doctor" (

) ... but he was from a more formal generation, more formal schools, where my own age group was at the cusp, one foot in formality, one foot off dancing with hippies.
On the other hand, I'm not there in your class, don't know him.