That sounds like a little passive aggression to me, but whatever.

I think most people use those sound rooms to get an idea of what each guitar (or amp) sounds like, and that's kinda hard to do with someone else making distracting noise.

I think it would be best to just ask if the other occupant minds before picking up a guitar. Communication is easy.

It's hard to tell without knowing exactly what he said and the tone of voice, but he was maybe being sincere? Maybe you have a knack for it, or you just seem like you know what you're doing, or maybe he's even newer than you and he's choosing the guitar he's going to learn on.

It's not impossible he was being passive aggressive, but that seems like a weirdly elaborate way to go about it.

Best this ask the store, they would know the etiquette their guests expect

In the room within the room where everything is priced upwards of $3000, where there's usually like 1 bench and like 12 guitars... yeah.

The regular room? No.

if you actually played a few for them then they where sincere but I feel like even someone who doesn't pick up on social cues could figure that out.