It is possible they just decided to switch sides, or they're role playing as dual nature. Doesn't make much difference but I still say we err on the side of caution: no FAKs, no revives, don't talk in front of them. If they are a spy it's sensible not to waste resources on them, and if they're a survivor we're probably still doing them a favour by ignoring them which might encourage them to leave. After all, this is probably the suburb where people are least likely to trust someone with that skill set and plenty will just PK them, and given their lack of survivor skills they can't be any practical help to us except as fang fodder so there's no benefit to us in not treating them like a spy.