This is not true. Counterpoint, responses like 404 or 503 Bad Gateway do not come from the destination server. They do not indicate the intended server received your request.
Hmm are these assumptions valid? Can't a misconfigured load balancer cause a 404? Couldn't a bug in nginx, node or an app server produce a 500 response outside of your control?
I suppose a misconfigured load balancer or nginx instance could return absolutely anything. I think you'd have to be actually maliciously misprogramming it, though, to reach that level of dysfunction!
The former when the problem is on the client side, the latter for a problem on the server.
And you can still send a descriptive body for the error, if you so choose.