He's referring to the tabs under the thread's title. There is a tab that reads "Read Question" and "Reply to all".
When it is posted as a discussion, it reads "Read Discussion" and "Reply to all."
That's how you can tell what type of thread was started by the originating post and whether there will be a ribbon award option for the orignating poster to award to a response. The ribbons are only available to question type of threads.
Here's a screen shot of a thread that was started as a Discussion thread. Notice the difference? The tab under the thread title here says Read Discussion.