The member's table has leaked at least once, and the forum has been hacked multiple times. Your registration IP address and your last recorded IP address as of when the members table leaked is more or less public information now. An unknown amount of additional information from the other hacks is potentially essentially public information as well.
I'm well aware that to be the case, but the OP registered well after the known database leak which I believe was in mid 2015. This is also why I mentioned it's not much of a big deal due to most IPs would have changed by now as you said here:
a user's IP address will have changed after several months (and to a much greater extent, after multiple years) anyway.
First of all, I admire you for having the guts to continue engaging with crypto and also for not feeling discouraged at all despite the fact that it is banned in your country. At the same time, I'm a little bit worried to you because you may possibly punished by the law if ever you are proven guilty.
I'm not a total geek about computer stuffs but what I can suggest you is to use a VPN to hide your IP because that makes you anonymous everytime you will access the internet. I hope it helps.
This is also generally bad advise. Just because you are using a VPN doesn't mean you can trust those behind it, especially when confronted by a government authority they may release the information without even putting up a fight.
No log VPNs are good practice, but even these in the past have been caught keeping logs. Even, if you use Tor Browser there's speculation that a lot of the end nodes are actually NSA owned.