The ban is on the IP+username combination; the actual forum account hasn't been flagged.
I can't find any information on what triggered the three banned IPs either, but it appears that while you registered your account and made most of your posts from IPs in one country, the IPs that got blocked are assigned to a VPN provider in another country, and that set of VPN is often flagged due to folks using it for all sorts of suspicious activity (widely reported online fwiw).
If I had to guess, I'd say the forum automatically banned those IPs for repeated login failure attempts, but I don't have server logs going back far enough to confirm one way or another.