There seems to be one of those in every class (ok well not EVERY but it's common). I went through a short program and in the class was a guy, Brian, who clearly thought all this classroom stuff was beneath him, and frequently spoke up in class to let everyone know how knowledgeable he was. At one point Brian said something outside of class about how he was self-taught and had been in the field for a while, but was only taking this course as a technicality. He also frequently made references to being "a bit older" (in the tone that suggested "and therefore know a lot more"); I think he was 24 and the rest of us were maybe 20-22.
Later, a bunch of us from that program all got part time jobs in a place that really didn't use our skills to their fullest degree; most took this job as a summer job to help pay for the program we were in, and a few of us stayed on a little longer, after completing our program, the job market being rather dismal at that point. It wasn't a horrible job; it paid okay wages, but admittedly it wasn't the type of job most of us had envisioned going into the program.
Brian was one of the ones who stayed on in that job and I worked with him. Again he seemed to feel it was beneath him, and at one point he said to me, "I'm really only doing this as a favour to Jim." (Jim being head honcho of head office).
It was all quite a long time ago, but Brian would have been the type to ask the instructor to "explain to the rest of us." It's very condescending. And a sign of insecurity, IMO, when you just HAVE to let everyone else know how much more you know than them. I've been in situations where I've had to sit through material I was already familiar with, and unless someone specifically asked for my help I just shut up about it.