First, I don't think Trump showing up at the caucus site when Beck was there was intentional. I sincerely doubt the Trump team is tracking Glenn Beck's personal appearance schedule.
However, once he was there, he could have waited until Beck had finished spewing his line of BS, and then entered the caucus room.
Not doing that was a bold and Trumpian choice. It was awesome!
Maybe, just maybe, Trump wanted to save Cruz from Beck and that's why he didn't wait. It's possible he did Cruz a favor.
OTOH, maybe all those people were there for Trump and were just bidding their time listening to beck.