I can't imagine ever assuming what someone else's salary must be. Even if it's a matter of public record (as in a non-profit org or public service) it's one thing to discuss it, but still rude to bring it up in such a confrontational manner.
I remember a time when I was walking down the street in the Big City I used to live in. I admit, I was feeling quite nicely put together that evening, but it was still nothing special. Jeans, sweatshirt, sneakers. A man sitting outside the church (usually a place for panhandlers) said, "You must be a millionaire." Uh, what? No, actually I'm a college student with no cash. What an interesting assumption!