They're describing the site content, telling you that the site is pornographic and really youth endangering etc. and they're going to put it on a list of youth endangering media beside you have any reasons to think that their decision is wrong.
If they'll be able to enforce blocking all sites on their list some day you won't get any german traffic to that site anymore but I doubt that is ever going to happen.
You won't get arrested if you enter germany.
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