Hand in pocket can mean a number of disparate things, depending:
- I am a cool person;
- I do not care/I am better than you;
- I do not know where to put my hand and am embarrassed letting it hang around (check out Merkel's famous Hand Triangle as an alternative strategy).
Depending on presenter type and assuming it's not 2., it is perfectly fine to put the hand into the pocket. I have never seen anything berated for this, and in my opinion the foreign student was totally out of line. I thus assume the presenter belongs to group 3, because if they were 1, i.e. the cool guy, they would have found the words to put the heckler in their spot; and if 2, being heckled would not have bothered them in the least (I assume via the question that they were bothered).
Maybe it's a cultural thing, but the heckler was the foreign person and thus should have been doubly careful to berate someone on unfamiliar turf.
That being said, hand in pocket may come across as haughty or snobbish, and is thus not usually recommended in presentations, unless one is really sure that it sends the right relaxed and comfortable attitude (aiming to induce similar relaxed attitude in the listeners).