@neil hmm, not knowing the crowd and format, but it sounds like a pattern i have seen at other conferences: not enough space outside of halls to sit and work on a laptop, so people go to not filled sessions (and they are not interested about) to sit and type and ignore the talk.
Often this (not interested in topic, finally some room to sit) goes hand in hand with a lack of care for silence.
This is me guessing, but maybe this can provide you with a new perspective.