Is it true that only girls use うち to refer to themselves? Is it true that only girls will use to refer to themselves? So when a guy say he is referring to his in-group / company / family, and not referring to himself, right?

is mostly used by girls to refer to themselves, but this usage is only common in Kansai-ben and perhaps other regional dialects as well, and it is generally not considered to be part of standard Japanese. See <

So to answer your question, yes if a guy says , he is probably most likely referring to his family. (Assuming he is speaking standard Japanese, usage in regional dialects may vary, but I know in Kansai-ben it is generally used only by females)