One of the biggest issues people initially had with AI is that it’s trained on copyrighted material, but really it’s not that big of a deal. Humans are trained on copyrighted material whether we realise it or not. Everything we’ve ever experienced influences our decisions, and therefore our designs.
This is where Cryptomnesia comes into play. Humans often copy others work without realising it. We’re creatures of imitation and it allows us to blend in with group. We’ve evolved this way to protect ourselves from social danger. That’s why it’s not really surprising that design trends exist, or that humans are capable of copying each other without remembering that they saw the idea elsewhere.