He's not surprised, not really, when he looks back through the doors to see Tris is still on the mats like the world isn't passing by on the outside. Bellamy doesn't have much of anything else to take up his time, and besides, he has Raven to check in on and generally pester on a daily basis via phone in addition to Clarke.

So he grins when he sees Tris looking out at him, and waves. He's going to give her shit for it, but he doesn't mind.