By right PLA should have intelligence on impending Indian offensive and be better prepared than to get caught by surprise
The general pattern of previous Indian Army clash with the PLA in the last 20+ years have been pushfests and some brawls. There were no recorded fatalities, and all had been resolved relatively peacefully through negotiations.
The PLA could not have predicted Operation Snow Leopard that easily. Imagine if an agent were to give a tip off that the Indian Army is planning to commit murder during a negotiation. To the PLA high command, that would have been unthinkable at that time. Why murder a PLA negotiation party and risk starting a war with a superpower? That would be like the Syrian Army suddenly ambushing and killing US soldiers without provocation. It is militarily illogical. But is it still feasible? Yes of course, if they are really that stupid.
Perhaps the one mistake that we can blame the PLA is underestimating the stupidity of the Indian Army. But its still not an unforgivable mistake. I don't think that many outside of South Asia could truly comprehend Indian stupidity.
Nevertheless, after recovering from the initial shock. The PLA did come back in force and thought the IA a lesson that would scar them for decades to come. India chickened out of a war after that, and they had yet to repeat such stupidity. So lesson learnt for now.