Glen was more upset by the user rating (formed by the public, not critics). At the time it was sitting at 1.7. Metacritic's users were making a statement. Not necessarily a truthful statement, but a statement nonetheless.
Schofield wasn't happy about this, so he hit his twitter feed and posted: "I don't usually do this but, if u like MW3 go 2 Metacritic.com & help our user score. It's suspiciously low. Be honest but help if u agree."
He's since deleted the tweet. Probably because it got him into trouble. Later on, after some negative feedback and accusations unfair boosting, he attempted to justify his original comments by posting that he "know[s] it's better than a 1.7."
It seems the users agree; Modern Warfare 3's user rating currently stands at 1.8.