It’s a matter of notice and the essentially automatic nature of such image displays. Let’s say you have an IB account, likely required to even view the image. And I know when a character looked at my character. I can make a good guess at what IB user owns what Wolfery character by matching up access IPs. If the URL is there people can make an informed decision and the timing is delayed, use a private window with an alternate throwaway account, etc.
Obviously I have special access to IB and it is unlikely I would actually do that but it’s not really good to allow that possibility for anyone. (This is also why IB uses its own VPSes and machines for content hosting rather than proxy through CloudFlare or the like.)
I suspect the two matters are separate, although one may have prompted re-evaluating the other.
That said, Hetzner’s terms include the following:
This is more specific about certain aspects than e.g. OVH’s equivalent content policy (section 7.2), albeit still subject to interpretation (are they saying all porn is illegal, thus forbidden, or all illegal porn is forbidden?). As always it is the actual enforcement that matters.