GX7 vs E-M5 test. Curious, they have different sensor sizes?

Image courtesy DSLRmagazine.

DSLRmagazine (google translation here) compared the new GX7 vs the E-M5. The tester writes that he expected a better result from the newer GX7 sensor. The image quality is more or less on par, the E-M5 has a better saturation and clarity, and the GX7 looks a tiny bit better at High ISO settings. They also discovered that the sensor size seems to be slightly different between the two cameras. The GX7 is a tiny bit more wide angle compared with the E-M5 (same lens used). Here is the GIF that proves it:

Do you know guys why it is so?