Last year I had a prof who denied the existence of adverbs, and instead posited a class of words that were labelled "intensifiers". Many words that would have been otherwise been labeled as an adverb were then labeled as an intensifier. What's the point of the label "intensifier" in the first place, compared to "adverb"? To me, they seem to be two different names for the same thing.
Categories are defined on the basis of distributional equivalence, so there are two possibilities here.
- Your professor thinks that intensifier is a better name for this particular category than adverb is, more or less in the same way that some people still use the somewhat dated substantive instead of the more common noun. This means that he's just taking issue with the names we assign things, not with the actual existence of those things.
- Your professor believes that the category of adverbs hasn't been properly defined, in the sense that it includes items that are not adverbs. When you correct this mistake, you are left with a different set of lexical items, and he's using the label intensifier to refer to what he believes are the correct items that belong in this category.
It's difficult to tell which without further information.