We're basically looking at b787's aggressive pro-Russian sentiment, when the JF-17 is a 3.5 generaton aircraft that's essentially a glorified MiG-21. The latest JF-17s have fully upgraded radars, of course, but the difference in diameter size means that the J-11B, even with pulse doppler, is going to outclass the JF-17 BVR.
We also do not know the rules of engagement of the dogfight or the specifics; the JF-17 pilots could have been newbies while the J-11BS could have been top-tier, while the J-11BS might have wiped out the JF-17s in a BVR engagement, where the smaller JF-17, smaller than a MiG-29 or F-16, would be at a gross disadvantage.