@Acolytus I'm just going to pull this out of my arse, but my best guess is that they were used in the same publishing company as the original novel
I doubt a company would file a lawsuit for using copyrighted characters in other works unless it's terrible or is providing unfavourable persuasive opinions on them. What they're doing here is basically free advertising in a way.
If this weren't the case, studios like gainax would've sued a lot of other companies by now because a lot of their evangelion references goes directly without any form of censorship or attempts to mask the references.