Body language: is this true (pls read on)?

Question:

Someone told me that in Japan people nod their heads (up and down) to say No while they shake their heads from side to side to say Yes. Is this true or is my friend having me on?

Answer:

I am sorry if I misinterpreted your sentence.
We do not nod our heads when we express NO.

It is opposite.

We shake our heads when we mean No.

For lots of Japanese, Nodding heads means “ Yes. I am listening. ” .

I am Japanese and my partner is Westerners.

He took long time to find out the difference of body language between Japanese and Westerners.
He misunderstood me so many times.
I was nodding my head and I meant ‘’Yes I am listening.” but I DID NOT MEAN “Yes I understand.” or “Yes I agree with you.”.

also,
see following conversation below
A: Are you interested ? (Anata wa kyomi ga arimasuka?)
B: Yes, I am. ( Hai, Arimasu.) or No, I am not ( iie, Arimasen.)

If you ask Japanese people “ Aren’t you interested? (Anata wa kyomi ga naino?)” , Tthey might say YES(hai ), I am NOT interested.
I know it is funny but this is ok in Japanese.
It makes sense in Japanese grammer. We can understand what they mean but in English, it will make people confuse.