You do understand China and Vietnam actually fought each other, yes?
Long time ago, but still.
“I’d rather smell French s___ for five years, than Chinese s___ for a thousand.” - Ho Chi Minh
Also, Pol Pot was an ally of China, and it was Vietnam that put an end to the Khmer Rouge regime.
Just how many people observed that border skirmish?
Commies fight each other all the time. Goes back to Bolsheviks versus Mensheviks, Stalin versus Trotsky, ad nauseam. No communist will ever fight to make the bourgeoisie more secure.