"Hey Donnie!" By now, Lopmon is pretty sure he knows who got messed up by the virus and who didn't. If Kovu could forgive him for being some part of the virus itself, then he could forgive Donnie for the stuff that happened while it was going on. That's what Kovu was trying to do when he was talking to Fluttershy's friend, right?

Strabimon hasn't met these guys before, he only saw the guy on Kovu's D-Terminal. Kovu was tight-lipped about him as he is about everything else, so the wolfish Digimon just keeps himself off to the side, letting Lopmon deal with him.