One popular usage of the flag was "gay pride". I would argue that the recent association is more with the LGBTQ+ community. There are conflicts in the lesbian community between lesbians and transgender people, so it's not really a flag of the homosexual community as a whole either. Indicated by the addition of Q and + it also might have a meaning of progression. If you look at the wikipedia article there are other flags that look very similar.
Why is this relevant for the subject at hand?
I would argue that the people who design flags for such successful movements are highly intelligent and educated, and understand that symbols need to have deeper meanings rooted in culture, history or even religion.
So why is the rainbow flag appearing alongside with the appearance of global banking? I have no clue. All I am sure is, that the meaning is more complex than what you have suggested. Is there a concious connection the actors of the global banking system see there? I don't know.