It is possible that they were carrying live rounds. Practice IR missiles usually don't have transparent apertures for IR sensors. Then again most PLAAF practice rounds are blue. Not sure which is which.
I believe they should be training rounds -- live PL-8s have had opaque apertures as well as transparent, and for training IR missiles they should have the same seekers as live rounds.
Some PL-8 variants have opaque/white seekers, and live rounds and training rounds both follow suit. Some PL-8 variants have transparent seekers, and live rounds and training rounds both follow suit.
In the case of PL-10, it has a transparent seeker, so live rounds and training rounds would both follow suit as well imo