Why would Oklahoma fans get angry with Westbrook? He is on free agent so he has the authority to not sign with the team and go sign the other. It's business man, and its in the rules of the NBA and not just the players decide with that rules.
You can't blame the fans, when Durant leave OKC, that's the same thing they felt but they also felt it with westbrook as fans really wants their player to stay if they like it. WB is the main man of the OKC for many years, the fans supported him although they are not as good as during the time of Durant and Ibaka, but when he decides to leave, that makes the fans upset. It's understandable that it's all business, but fans does not feel that way, they are more emotional when it comes to idolizing their best player.
But fans won't understand this for a bit, so it's going to be interesting to see WB first game in Houston uniform against OKC this season, it's going to be huge.