I think we need to be slightly more calm and pragmatic in our assessment of the situation.
I think there are rouge elements within both China and Mynmar that are seeking to escalate the situation to their benefit.
When trying to assess a situation, the most important thing to do is to establish the 'why' of it.
We have to assume that at government level, people do things for a good reason (at least from their POV) and not just out of spite and/or incompetence (mind you, that also happens, but is thankfully rare, and so can generally be easily noticed).
So let's look at the 'why' behind Mynmar bombing Chinese territory.
What has made analysing these incidents so hard is that it simply doesn't make sense for Mynmar to do what they did. Repeatedly dropping bombs on Chinese territory and killing Chinese civilians, well that's indefensible no matter what the reason or provocation.
Never mind that Mynmar hardly has a cosy relationship with the west, even if this was a major western ally like the Philipines, it would be hard for anyone to say much if China took retaliatory military action, like levelling the airfields the strikes were launched from and imposing a NFZ over the entire area.
There are only two semi-plausible explanations that I can think of.
1) The bombings were intended to send a message to Beijing, and the civilian deaths were an unfortunate accident.
From Mynmar's POV, the insurgents are 'ethnic Chinese' as the western media loves to call them, even though Chinese is made up of 56 ethnic minorities, and the people involved are one of these minorities, and not from the Han majority I believe.
They had connections and families in China, often hold Chinese passports. They are getting aid and supplies from those contacts inside China, and frequently hope across the boarder to escape Mynmar troops and launch offensives from Chinese territory.
All of this is often done with local government knowledge if not support.
The Mynmar junta knows about the internal political situation within China, that local governments have a great deal of autonomy, and sometimes overstep their remit and do things the central government most certainly do not approve off.
Thus, the shelling and bombings might have been a desperate attempt to draw Beijing's attention to the situation in the hopes that the central government will take notice of what the local government is doing and put a stop to it.
The intention would have been to just put some craters in a couple of fields, and it was an unfortunate coincidence that people were working the field they bombed.
This is plausible, but not all that likely, since you would think using standard diplomatic channels would have conveyed the message to Beijing effectively enough.
That leaves the second, more likely scenario.
That the bombings were a false flag operation by the rebels in an attempt to draw the Chinese military into the conflict to obliterate the Mynmar government forces for them.
Obviously the rebels do not operate fighter jets, but they could have sympathisers within the military who are either pilots, or ground crew who could potentially supply the pilots with false co-ordinates to attack.
It would not be the first time someone tried that trick.