No, they didn’t have to be enthusiastic - and several of them were just sitting there - you could see the audience behind Cruz, and there were a few who didn’t seem to be participating.
And .. I believe the President of the school said as much. The students do not have to applaud or stand, they just have to be there.
They run three of those a week, which the media usually “forgets” to mention that.
I saw more than a few red-shirted Paul supporters applauding and standing up for Cruz.