It's hard to tell from the article, but I don't think there was any change in Chase's advertising spend. My interpretation is that they are spending the same amount, but restricting bidding to a whitelist of sites.

If so, the fact that they don't see an impact in # of impressions means more about the ad exchange's bidding system and inelastic demand (or lack thereof) for inventory on those whitelisted sites.

I don't think this has anything to do with fraud.