Steven Universe - "It's Just Light Brites!"

Ah yes, the Mooninite bomb scare. IIRC, the president of Cartoon Network stepped down because of it, and he was replaced with the guy who thought CN Real was a good idea. Kinda makes you wonder how different Cartoon Network would be now if things had ended differently.

I feel completely in the dark here. What are these things in the picture? What's this about a bomb? What happened at the CN?