Don’t want to defend that user but its not that cut clear if he/she is the one behind that download link. Your reasoning sounds logic but realty is often not that logic. What’s clear unfortunately is your promoting a free download link to your product and advertise a pirate website on the CGtrader forum. Probably not what you intended but result your mostly getting right now.
Also note if the user with that name (or different one) purchases something from anybody then that seller can’t do anything to prevent a download, so your warning is completely pointless.
Probably best to request to remove this post entirely?
Send message to info@cgtrader if you like to do that.
PS: Send DMCA takedown to those site administrators (https://kinsta.com/blog/dmca-takedown-notice/) note CGtrader can provide you a standard notice.
Take care and good luck,