All he said is that Arsenal were chasing a big player and Lord Harris confirmed this. Someone at the club told him that talks were under embargo and Benzema wasn't signing. He doesn't seem at the top end, but high enough to know a fair bit. He hasn't made any bold claims.
Oh come on mate, I could have made that claim by using common sense. All the big clubs are chasing major signings. It's very easy for me to sit at home and tweet that Chelsea are chasing a major signing in Pogba and gain the adulation of twitter. Color me impressed when he actually calls a signing before anyone even reports it otherwise he is just another one of those ITKs