Don't forget that examples listed in records are typically only the tip of an iceberg (or so I'm guessing, as I'm hardly in a position to know anything useful). That means there's a lot of other creepy comments the user has left lying around that show a persistent pattern of poor behavior.
If I had made the comment you link to, it's likely no one would notice or care. The moderators would look at my other behavior on the site and figure that I just made a hit-or-miss attempt at witticism that was a complete miss. At worst, I'd likely just get a warning via PM that I wasn't quite as clever as I thought I was. Flubs, goofs, and verbal faceplants happen, and the e621 administration know this.
On the other hand, the user you selected as an example appears to have habitually made creepy comments galore. Warnings were apparently ineffective as were ensuing records. The admins didn't ban them on a whim and then simply ignore any potential appeals of that ban.
Admins don't just look at the one problem comment. They have to take into account the user's other comments and the context behind those comments. My one hypothetical screw-up of a comment is hardly comparable to the cited user's long term pattern of behavior, deemed constantly creepy not just by admins, but also other users.