Lol, Baseball Reference WAR is the one that has Barney as being very valuable at that point. I'm pretty sure there's a reason why people on this board rely more on fWAR. And btw, I don't see how it's that big of a deal that Barney may be above some in WAR at one point in a season, he's an elite defender, if he could hit for 100 wRC+ for a period of 3 months it wouldn't be completely out of the blue to see him above someone like Cabrera, who maybe was having a few down months (not that this happens very often or did happen in this case) and everyone knows that he's a horrible defender, specially at the hot corner.
By the end of the season regressions have likely happened and then Barney goes back to hitting abysmally and Cabrera makes up for the first months by being a beast again.