Let's concetrate on engines and ignore the fact China has at least two stealth fighter programs...
I'm reading a lot of reactions doing an internet search. I especially like the ones, yes there seems to be a common ignorance out there from self-proclaimed experts, asking if any of China's stealth fighters, including the J-20, have even flown, ergo, they must be just mock-ups to fool the West. I read another article that said China can't make a reliable domestic engine they can trust to put on a single-engine fighter, so that's why their stealth fighters have two engines. We see them on J-10s. Oh yeah let's leave out that fact so the conclusion made before writing looks true.
It is obvious the engines powering the J-20 to skies are not AL-31F engine.