We had a similar problem with a talentless rogue designer at my old agency.

It only became clear he had blatantly copied other sites after he left, unfortunately (he was also sacked from future jobs for the same thing, I suspect).

He even had the audacity to claim an award for one of his rip-offs, including attending the vegas ceremony (IIRC). I really don't know how he slept at night.

I'm not going to name names as this was a long time ago and I'm hoping he's changed his ways.