thanks for doing

As this is spoken English, commas are irrelevant. In a transcription they can only indicate pauses in speech. Thus think the most likely reflection of what the teacher said would be :
Thanks Peter, for.....
but the two pauses are certainly possible.

But why do you say the teacher is not addressing Peter?? it seems to me s/he is. If s/he was "announcing" something, it would be to the whole class, and s/he would say :
Thanks to Peter for...

Good answer. Thank you.