I wouldn't be too worried about it. I would celebrate his crying. Give him a good round of applause and a big fat cheesy grin all the way to the playpen. Let him have some "me" time and don't take him out until he can settle himself. If he winds back up when he sees you then put him back and start over.
He's two and a human being. He is just expressing his little feelings. I think that's a great thing. The only issue with expressing them with crying is that crying is loud so it's best for him to have an area where he can be loud without affecting the listening ears of you, your children, and the other kids.
We put way too much stake in crying. Instead of trying to get it to stop... I say cheer it on and celebrate.Give him some finger snapping a round of intense clapping and smile smile smile. Have the other kids join in. Maybe a little dance moves.... and a wooot wooot wooot. Praise him for being the best cryer ... "you cry GREAT little buddy. Get your cry on"
It's the opposite reaction he's used to... he'll get the picture quick like that you don't mind a bit if he expresses his little feelings.