In my experience, it does have different meanings.
One usage makes me think of: "friend", "close friend", "homie", "my guy", "dude", "someone I trust", etc.
Another usage is: "immature", "douchey", "fake", "asshole", etc
Understand that bro also has a pejorative connotation in some context, but that is not the case here.
If the quote was "we are operating as a fking unlicensed securities exchange in the USA brother." how is the meaning different?
I can see that they have slightly different connotations like thanks versus thank you, but that doesn't mean it it's no longer an abbreviation, which is what the parent poster was claiming
No, but it would be unusual. You don't hear people using a term like "crypto brothers", for instance. "Bro" carries a different connotation, and it isn't a positive one in this example.
I don't think it is simply an abbreviation in this case.