That's just steam being steam, they always ban some +18 game with that reason, even if there's no young looking characters. My Dystopian Robot Girlfriend also got banned from steam for the same reason, when clearly there's no characters that are or appear to be underage in the game. The worst part is not even the ban, the problem is that you can appeal or even remove the "problem" and send another request for steam.That doesn't really make sense, considering the fact that Karryn's Prison (which has goblins) exists, Breeders of the Nephelym has shortstacks and size randomization, both of which are on steam, and there are quite a lot of other games on there as well, that are nsfw, which have size randomization which goes into the negatives from the base size.
It all just centers around what the dev makes the standard for the possible characters.
And even then it sounds like a weird reason, because that would imply having to add more things to make a character seem "young".
Sometimes, some games get past this problem, probably due to having publishers behind them, who can appeal to steam.