Most of the backdoors I have seen even in examples of the "backdoored" Chinese equipment can be described by Hanlon's razor just like in Rigol's smtp case.
Never attribute to malice that which is adequately explained by stupidity
I know, that's why I said "paranoia".

That said, lousy security can be a very serious problem in some environments.
People get paranoid because of the "Chinese" boogeyman (not to say there isn't a threat), but I've seen as equivalent stupidity from American equipment vendors, even big names like Cisco are part of it
Of course. Getting it right in a big company is very hard. Especially when everything was just soooo coool, dude, in happiest times!

Straightening poor practices inherited from the past is really difficult.
Just reinforcing the point that you can't trust any piece of networked hardware from any vendor period.
And indeed you are right. My commment deals with the trust problem that these new manufacturers can face. They are newcomers, they are beginning to sell somewhat mature products and nowadays people pays much more attention to this crap than 30 years ago.