There seems to be a glitch where if the TV says there's an outbreak of surskit on route 120, there'll be there.. have you exchanged records with someone who has Ruby resently? I think that can cause it.
14. Q: Hey! Surskit's not supposed to be in this game! What gives?
A: No, it's not. But there seems to be a glitch where, if you mix records with R/S, you can get a "swarm" of them on a certain Route, just like you can in R/S. Just go with it. It's a good thing.