Is 「何もしないで暖かくする」 ambiguous?

Question

I was reading this answer and I came across this:

(A) 何もしないで暖かくする (ambiguous)

(B) 何もしなくて暖かくする (unambiguous)

I'm not sure why A is ambiguous, but here's my understanding: unlike なくて, ないで doesn't imply a cause, so it could either mean that not doing anything keeps you warm or not. However, in the same answer, it says that B does not mean "keep the body warm by not doing any activity," which contradicts what I know about なくて, that is, it implies a cause. In other words, I would translate both as follows:

(A) 何もしないで暖かくする。

Somebody doesn't do anything and keeps warm.

^{not necessarily Somebody keeps warm by not doing anything.}

(B) 何もしなくて暖かくする。

Somebody keeps warm by not doing anything.

^{not Somebody doesn't do anything and keeps warm.}