Some googling yielded this, for example:
But this only shows that there are some regulations and licensing required, no details unfortunately.
And, first of all, I'm not even sure if it was the ME firmware or any firmware at all. Might have been some stupid application you install on Windows.
I wouldn't buy security-critical stuff in China. You can bitch all day long about the US, but the fact is, if something like this San Bernadino phone unlock case happened in China, with Chinese phone from Chinese vendor under Chinese jurisdiction, you probably wouldn't even have heard about it.