Luckily, with given information, the whole bug hunt thing was super vague and could be translated in multitude of ways. And yes, one way it could imply that the marines have dealt with alien lifeforms before but nothing more serious than routine pest control, these pests might have even been nothing extraterrestrial.
Bug hunt may even have been some slang term for missions that sound dangerous but turn out to be nothing.
Whatever it was, in relation to the xenomorph they were largely meaningless.