@Balancegrim
Possibly, but he has no proof and he has no good idea about how the legal system works. If he killed them and they turned out to be citizens in good standing, he might be exiled or otherwise punished just because that's how the laws work to protect citizens from adventurers. Might even apply to him beating them up, so running away after beating them up might be the better part of valor.
(Even if it seems like there's two guild-affiliated witnesses)
Also he doesn't know if they are more than scary hoodlums, so killing them would have been his escalation. They might have been using threats of rape just as a way to extort more money out of what they assumed were weaklings with too much money. Or they really were as bad as they seemed, but given how orderly the rest of the town seemed, and the lack of comment from the guild guy about it, this doesn't seem overly likely from a mid-day assault.
tl/dr They're probably crooks, but MC ain't no Judge, Jury and Executioner.