The mere fact that your bird stood out from the 'crowd' so to speak suggest you may have called it right. Your bird appears to be in reasonably fresh plumage so one would expect Mongolian to show warmer, more rufous toned and heavier streaked upper parts. The limited view of the breast appears to lack fulvous tones but a front-on view would be preferable for confirmation. Do you have any shots with other birds from the flock, a comparative image would be useful? Failing that, did you get any images of presumed dukhunensis from the same location with which to compare?
For future reference, vocalisations are different so even if you do not have the proper sound recording gear you could try and obtain a useable recording on your smartphone, assuming you have one.
Grahame