It wasn't their fight. They should have stayed out completely but they still stuck their nose. One of the biggest learnings of our Ops was that 2-front war is a reality and we just weren't fighting PAF but rather PLAAF's B-team. What China did to help their puppet wasn't shabby. Some help was expected but trying to provide live satellite feed to target our fighters or S-400 was going too far in my view. They also provided PL-15 from their own initial batches(from 2016) rather them giving them the export PL-15E version.
I have been reading about 2 front war from way before opening sindoor. The books, analysis are even older. I assume military higher ups would've started considering this even earlier.
For reminder, Galwan was very recent thing.. both the armies were in kind of a standoff. The geopolitical battle was out in open, and we had made clear that gone are the days when India will not do anything. I am pretty sure, IA wouldn't have been withheld from firing back if situation arose.. ( important point, since earlier even western front wasn't free).
In that kind of situation... That's no backstab. It was a frontal slash.. and let's not kid ourselves that they would've limited their roles if we had shown weakness.
It was precisely because of our success in destruction of initial targets inspite of their domestic PL-15 followed by their defence network dismantling, further followed by grounding their air force and hitting deep... That the Chinese limited their roles both militarily and diplomatically. Even started taking the de-escalation at LAC as crucial.
That is just to clarify the thought process that this was something out of ordinary. Not!
Why wouldn't they track our systems? Wouldn't we expect our forces to keep track of their movements even in normalcy.. let alone when their forces are on move ( in any direction).
I don't believe it was unexpected or out of blue for higher up. Sure, it happened for first time, but that's because this was our first considerable military conflict since 1999.
It's just like let's say taking a cold shower in winters... You know it's winter, water is chilly, you must have thought you would make it quick.. you are ready but still when that first waterpour hits you, you freeze. And then you carry on.
That's all. Were you caught unawares? No. It's just brain being brain.
Your conclusion, that we were caught unaware or it was unexpected would be valid if there were signs of fluster in chain of command ( system) , anything being some in a hurry etc.. but the fact that the system and plans effectively carried on should be proof enough that it was expected and personal shock didn't hinder military actions.
At last.. since when it wasn't their conflict? From srilanka, Maldives, pakistan, Bangladesh.. We have been in conflict with them since a decade now. Guns were fired? Well they weren't fired this time either.. on the border it matters. A micro cold war.