I know that players like to have a chip on their shoulder and sometimes revel in a "revenge" game, but in what world does Diggs live in where he thinks this team didn't believe in him?

This is some seriously skewed ego-fueled perspective from Diggs if that's a true statement. Sure, Zim may have not liked his attitude, but there isn't a single reason to believe that the Vikings org and especially the fans didn't believe in him. They gave him every opportunity to succeed, paid him when he was still somewhat unproven, and propped him up to be a face of the team.

Is he just pissed we wouldn't pay him the same amount as Buffalo?

I love Diggs, but man this prima donna shit is a super bad look for him.