I disagree that those cartoon aliens are "humanoid".  They look like Gummy Bears and have zero indication of boobs and/or genitalia.

However, I don't make the rules and if the admins say that they are "nude" and need a non-nude thumbnail, then there is no arguing with them about it.

The images can still be posted, just not a nude thumbnail. As Laurie said, all he has to do is make a new thumbnail with no nudity in it and check the flag "nudity" and all is kosher.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi