The definition says that you might refrain from either shyness (your own preference not to participate) or unpopularity (others' preference that you do not participate). I think the latter was more what was meant here.

I'm extremely shy in certain situations (for instance, I hate introducing myself to people at parties, bars, etc.), but if I'm in a meeting for a group I'm involved with, I will absolutely say as much as I'm allowed to say.