Is having your hand in your pocket during a presentation bad?
If you want a short and binary answer, it is likely yes &mdash; keeping a hand in a pocket during the presentation is not the best habit, because:


You lose yourself a chance to use that hand for communicating with the audience via gestures.
Your body language and posture is more likely to be perceived as you can't be bothered with what you are doing.


Having said that, there may be examples of excellent use of almost anything which is normally not recommended in a presentation, if you plan for it and do it consciously. For example, if you ask your students the famous Bilbo's question: "What have I got in my pocket?" &mdash; and put your hand in your pocket, your gesture is playing nicely with your explicit voice communication to create an interesting and intriguing setting.

A binary answer to your second question is likely no &mdash; students acted inappropriately by interrupting the presenter and commenting on the presentation style, rather than topic of the presentation. Unless, of course, the whole aim of the exercise was to receive comments about the presentation skills and strategies. From your question, we cannot tell.