I don't really know. My guess is that China have never intended to have photo ops for their tanks facing the Indian tanks at the border. What 'propaganda' the PLA showed off is still done with far less jingoism than how its done in India. Perhaps its down to the national policy not to inflame the situation too much. Is it right or wrong? History shall judge.What I am wondering is why did China agree to use these vehicles for the photo op and ceremony rather than the Type 15's. I can only assume that either China doesn't have as many Type 15's deployed as they claim(though if I were China I'd pull just 2 for this photo op) or they agreed with Indian to use older tanks so that it would play better at home to show the populace they pushed away an inferior enemy like the movies and not have them wanting vengeance or get too excited seeing a tech disparity between the T-90's and Type 15. I mean if it is the latter, it'll only work for so long before the Jai Hinds are asking why India won't just go on the offensive if China has inferior tech right?
Furthermore, as another member had said, the Type 15s are still not available there in large numbers. It only just arrived in PLA service. The PLA of the Western Theatre Command was until only recently, low priority. That's why they were still fielding many legacy tanks like the Type 88. It was out of necessity to put a sufficient tank force there. Rather than a perfect tank force.
So I doubt placing inferior tanks was done on purpose to give overconfidence to the Indian side. India won't need that anyway. Its media, the Bhakts, and the Jai Hinds are already bloated and bursting full with overconfidence. Luckily there are still cooler heads in India. Keeping that overconfidence from pulling triggers.