As far as I understand, C++ does not require NULL to be zero.
NULL is #defined as 0, meaning there's absolutely no difference except style/personal preference, and Bjarne "C++" Stroustrup was quoted earlier as preferring 0 (or nullptr in C++11 where available) over the NULL macro.
It can be any integer beside 0.
I can not remember where I read, but on some embed system, NULL can be a value different than zero.
So he is correct.