Huh a bulletproof bodyguard, that certainly makes much more sense (in relation to roleclaiming) than a doctor. That still doesn't explain why you weren't targeted for a night kill though (yes, you do mention that he may have scanned you).
Your argument that he knew that you were bulletproof is reasonable however it has equal chance both ways because you knew that he was being scanned last night, this leading to you shooting Salvage because YOU knew he wasn't bulletproof due to Sync's scan (no mention of BP). This allows you to frame Sync and get rid of him before he has a chance to scan you.
This argument can go both ways.
Currently I'm actually leaning towards Sync being town because, so far, his claims have all checked out while your bulletproof claim has as much weight as Salvage's claim now. Basically none. Either it's a ploy to avoid a shooting, using it as an excuse to not draw suspicion towards yourself or you are legitimately one (doubt and for good reason, see Salvage).
Those are my thoughts so far in this sleep deprived state.