The policy the above poster is referring to is No First Use [1], which is specifically about the use of nuclear weapons as a means of warfare. The Pearl Harbor attack, as it was not nuclear in nature, would not be relevant the No First Use policy if it were being followed to the letter and spirit.

How most nuclear powers would actually react to large-scale non-nuclear aggression is of course a whole different discussion.

1 - https://en.wikipedia.org/wiki/No_first_use