Given the timing, if such a delivery of PL15s took place, those would have been units pulled from the PLAAF’s own stocks, as not even China could manufacture a hundred advanced missiles in a few day’s notice.
Such a move is not without precedent in Sino-Pakistan relations, and I think a lot of people forget that and only considers such sales from a purely commercial POV, in which case it would indeed not make much sense for China.
Beyond the special relationship, China also have additional self-interest motivations for making such a delivery to Pakistan, chief of which would be to prevent all out war from breaking out between India and Pakistan.
Pakistani nuclear posture and policy is pretty much the same as that of NATO’s during the Cold War, which is to use tactical nukes to blunt the conventional military advantage of the enemy.
The only way to shot-circuit that escalation step would be to help Pakistan hold off Indian forces using conventional means only.
If the IAF suddenly started being on the receiving end of PL15s over Pakistan, beyond the material losses those missiles might inflict on IAF aircraft, a far more weighty message would be the strength of Chinese support and commitment to Pakistan in the face of an Indian invasion.
The unequivocal message to India would be that China would be prepared to do whatever is necessary to make sure Pakistan does not feel cornered enough to feel they have no choice but to use their nukes.
I personally believe that faced with the prospect of an all out nuclear war on its boarder that is perilously close to the source of many of China’s most important rivers and fresh water sources; Beijing would see a conventional war with India as very much the lesser of two evils.
From that standpoint, sending a hundred missiles really is loose change scale stuff.
However, if China did send those PL15s, I would expect there to be significant conditions attached in terms to secure storage and use limitations; as those would be PLAAF front line versions and not export models.
It could well be that those missiles are not sold or gifted, but rather loaned to the PAF, in which case they remain Chinese property, and potentially may be returned once tensions die down again.
If Pakistan can guarantee the physical security of those missiles when in storage, the risks to China of sending them are pretty manageable, since they would only give up useful SIGINT if they were actually fired.
When hanging off of aircraft, those missiles wouldn’t really give much away in terms of their capabilities or operating characteristic.
