I was thinking, if Vidalia hung around Amethyst and Greg for a time, then we can assume that baby/younger Sour Cream at one point hung out with the Crystal Gems, in one way or another.

Hey, he might of even seen the Gems fuse or something. If not, Amethyst morphing into something for Vidalia to paint.

So this might explain why Sour Cream was okay when Stevonnie separated on the dance floor. Seriously, everyone else was in shock but this guy was just casual and throwing around glow sticks all happy.

Dude, someone just turned into two children on the dance floor, and he takes it pretty well.