From what I read, they were ambushed during the negotiation with the Indians. I am wondering how could PLA tolerate such a despicable movement. They should pay the price!!
They did pay the price. The Indians had their commander and lieutenant both killed and possibly more seniors killed amongst the 20+ they admitted to.
They had over 40 Jawans captured with lower ranks returned the following days and senior ranked held up to a week.
Not even considering the 20+ killed (according to China, from injuries and exposure rather than the PLA's hand), that is the price they paid.
But it really must be said here that they were only defending what India considers their territory. Unfortunately the PLA had to respond with such a firm move back in Feb-May due to unprecedented levels of Indian intrusions into what both dispute. This isn't too different from the Chinese perspective who view the situation as defending their land from increased Indian patrols and illegitimate claims. The development was simply different and escalated differently with what seems to be China sort of determining where it goes with minimally effective Indian means of challenging as evidenced from Feb to now. I mean if during this whole year, the Indians managed to get the PLA out of finger 4 camps by force and capture from finger 4 to 8 and associated claims north of the lake, then yeah the Indians were able to reverse PLA's moves but they had a few tries and the only result was needless loss of life without strategic wins.
Basically a watered down summary is the following.
2019-Feb 2020: Increased Indian intrusions from Galwan up to finger 8 at Pangong.
Feb 2020: PLA was ordered to respond in one swoop to capture up to finger 4 and associated Chinese claim points to push out the Indians and establish at least a temporary control of all Chinese claims in response to India's slow but confident ingress into disputed parts.
Feb 2020 onwards: IA ordered to respond to PLA aggression and we have the clashes in May (original reports of confrontations everywhere including one where a large group of Indians were "subdued" and tied up with that photo) however there were plenty of confrontation events and points at which these happened. Also culminated in June fights under the lead of Babu. Following this, India continued to challenge PLA's move with ingress into China proper - Reqin, back in October to capture something to negotiate with. Promptly removed and the IA settled to within throwing distance of PLA's positions from Galwan to Black Top and Helmet top, removing PLA's range advantages if any. This prevents PLA from moving further as well, not that they did.
Now: Both sides agree to creating buffer in the dispute with neither side ingressing and building, patrolling etc. Done, PLA moves back and India also gets that win but India's original confident intrusions and increased patrols are also no longer conducted which satisfies China's wishes as well. Leaving this stretch to continue as a dispute... boring but admittedly sensible even for China.