1 - 3 : who knows
The reason could be any of them, or none of them. But at the end of the day I do not see any compelling reason for why the video's claims could not be possible.
Indeed, similar to the J-10, which was already flying for years and long denied, where it was clearly a AL-31 of some sort and nothing confirmed, we also here will know more some day ...
yes, but in this case my interest is much more limited -- i.e.: why does anyone think the video is somehow not accurate or believable.
Based on my assessment I think it's quite accurate and believable.
Agreed again, but my interest is not that limited, esp. since an answer to "what sort of DNA" this mysterious engine has would give some more details information about industrial cooperation or more.
To simply accept it is a "Chinese manufactured" engine is maybe no longer an question, but for me it is not enough.
Deino