What a curious thing to say, and you base your claims on what evidence?
On the contrary, on this case I think the more doubtful claim would be to suggest that the General had all the access to all the facts about J-20 to make any sort of comparison with any fighter in his own Air Force.
An equivalently unlikely notion would be to suggest the Chinese Air Force knows everything about F-22 and F-35 to be able to make an accurate and factual assessment on all of their capabilities.
That sort of intelligence is jealously guarded by both sides, and the default stance should be that no military force has the full spectrum of knowledge of either side's capabilities... and in the J-20's case it is only in the late stages of its development so the fact that the General is willing to venture out such a statement is premature given the full operational range of J-20's capabilities wouldn't even have yet been determined by its native air force!
Of course you're entitled to your opinions, but I find General Goldfein believable with regards to the J-20 being no match for the F-35.
Is that because that the General had said those words, or is it because you believed that was the case before he said it, or both?
Of course, I find all three of those options to be logically flawed.
I consider the General's statement to be empty posturing from a position of either accidental or deliberate ignorance.
I consider the actual capability of J-20 compared to F-35, F-22 or PAK FA or whatever to be essentially unknown at this point because we have insufficient information.