No legal grounds what so ever but potentially could bribe him, e.g. cash + game vega + new PSU etc. The way hs post is phrased really is odd, changed to some official AMD line about waiting for drivers and proper reviews.
the other explanation is as above, he was getting so much grief from frantic fanboys that he hust doesn't want to deal the stress, especially when he knows his system isn't ideal and he isn't an expert so it bound to make genuine mistakes.
Even on OCUK the usual suspects were complaining tat he wasn't using the right drivers when quite clearly he was and the version number matched the latest AMD FE drivers.
apparently the guy has been getting threats sent to him by amd fanboys, which sounds pretty normal from past reviewers getting the same to they don't praise amd.
probably had enough of getting "go die" emails and "hope your family gets cancer"