There is no surprise that communist China would and is supplying their northern neighbor.
If anyone is actually surprised about this, then maybe they'll be surprised when I give them an amazing deal of being able to buy the official deed to the Golden Gate Bridge for only $300 and a bag of salt and vinegar crisps. Just constant me at 123-456-7890 for details.
I mean, China is notorious for its foreign policy being primarily based on realpolitik rather than ideological allegiance, so the adjective "communist" before China is irrelevant to who they will sell weapons to.