According to the mod who posted the ban and the clarification:

Let's be clear about this: the material posted was, itself, not yet NSFW, which is why it's been left as a message to others that this is where the line was crossed. Rest assured, if anyone else had picked up on it and made it more explicit, that would have been deleted(...)The ban was for even suggesting fetish fuel material. Yes, we're that strict. Deal with it. Again: we are so harsh because idiots will keep trying to push the boundaries. Warning doesn't make a difference. We've even had people write pleading emails and PMs to ask for a permaban to be rescinded, which in a moment of weakness was acceded to. Guess what? They went straight back into writing almost straight-up loli porn. The mods have to deal with infractions of this type every day.

So, yeah, the rules are prett strict, probably because they have reason to be.