he didn't deny avogadro's number so much as say that its definition was somewhat arbitrary.
IIRC he made the comment before the modern redefinition of SI units. See https://en.wikipedia.org/wiki/2019_revision_of_the_SI#Mass_a... for more details about the ongoing issues associated with absolute numeric counts of elements and their association with mass.
this is useful context, thanks. would edit my prior comment but it is no longer editable. after some more research it seems his comments on the matter were reasonable