He didn't say "I was not an Inter fan", he mentioned Inter in a supplementary manner to supporting Cagliari as his local team. It was rather clear
<< Quella era la maglia di Ronaldo se non sbaglio ma ne avevo una anche di Recoba. Come ho sempre detto sono un tifoso del Cagliari ma ho sempre simpatizzato Inter>>
Like I've always said, I am a Cagliari supporter but I always had a sympathy with Inter. That's pretty much what this means. That he supported Inter as well.
The time he said he's not an Inter fan was the season before he signed, but we pretty much had him locked at the time. He was asked if it's true that he's an Inter fan and he said no, but his entire family is and he was always happy when they won.
I mean everyone was reporting that the reason Barella came to Inter and rejected offers from Juventus, Milan, Liverpool, Napoli and Arsenal was because he was an Inter fan... That was never disputed by anyone.
I don't get why you're being defensive, or offensive for that matter, in this case. It is a known fact that Barella has always been an Inter fan. Same way probably more than half of us here support our local teams as well. Just becasue there's a higher frequency his other team gets to play against Inter doesn't make him any less of a fan.