Actually, with an average BABIP (.309), because he's been able to keep the ball in the park (0.5 HR/9), his FIP is 3.57.....with, like Dipre said, improving peripherals, and not just in BB/9 but in K/9 as well. And this was against two very good hitting teams. It's a small sample, but it's also very common for pitchers to have something click a month or so into the season and their control improves.
His xFIP is 4.10, but that brings up a funny contradiction in FIP and xFIP. xFIP is based on what his FIP would be based on an adjusted (to average) HR/FB rate. But the whole concept of FIP is that you gauge the pitcher on what they can control (K, BB, HR). So, a pitcher who is doing a good job at what FIP credits him for, keeping the ball in the park, gets penalized by xFIP's normalization. Either the pitcher has control over HR or he doesn't.