Yeah, that seems like a different meaning, to be standing at a table seems to imply some involvement with the table, where saying "near" or "by" the table, that's just a thing you happen to be close to. I am American - does the question imply that "in" would be the more normal way to say this in British? Honestly you probably have a much keener sense of the differences than I do.
True, that would be the difference with the table. Anyway, Polish uses 'w' in this context, which is not a surprise, so 'in' seems like a natural choice. But of course 'at' is used with some places, at least in some varieties of English, so I understand this is one of this situation and 'at the gallery' is more natural for you. I don't really know enough about British-American differences, as a non-native, I tend to mix words and constructions from both of these.