Let's put it this way, politely: it's in the eye of beholder.

Most people don't find a random picture of an anime teenager to be harmful or have sinister implications.

Okay then, so don't read it? Do you have evidence this person did... whatever it is you think they did purely on the basis of theming their profile with girls from massively popular anime [0]?

From your profile description and that other comment, I would have assumed you were an ally. If so, I wouldn't have expected quite as much morality policing / thought crime tone. My perspective is that it's a little odd, but as long as they aren't hurting someone I really don't care what sparks joy in their lives. Life is hard enough.

And if they are hurting someone, that's what the law is for.

[0]: Their PFP comes from a manga / show that's sold over 10 million copies, apparently.