The flaw I see here is that the Rams strength is defense and special teams, so even if Goff posts some inflated statistics that should be elite but instead just end up making the offense average, the Rams will win. And like others have said if they don't win then it's gonna be on the defense most likely.
But to be fair he's correct that a system-based WCO (what McVay has shown this preseason so far) can make bad QBs seem statistically good, as completing a lot of short passes inflates QB stats. See Bradford's season, setting the NFL record for completion percent, 20 TD-5 INT ratio. It didn't get the Vikings anywhere, despite a top-10 defense, because every pass he threw went about 7 inches in the air. Not hating on Bradford because that's what he was told to do by Shurmer, and with not a lot of OL help they didn't have much else, just pointing out it is possible for a QB to have inflated stats, even set NFL records, and not post a winning record.
But again the "blame" if that happens here wouldn't be on Goff, it would be on McVay's scheme, or the OL, or something. Maybe that's what he was trying to get at, or maybe he's just a Goff hater, dunno. I'd probably shoot myself -- or better yet just change the channel -- before ever listening to Keyshawn.