It's got nothing to do with Secure Boot. If he had gone into the UEFI and disabled Secure Boot, the problem would still have occurred.
Secure Boot has become this scapegoat for everything that could possibly go wrong.
As its name suggests, Secure Boot prevents the OS from booting. If the installer is complaining about a product key mismatch, then it's got everything to do with the installer and nothing to do with Secure Boot.