Of course by simply calling someone ignorant, that of course makes it a fact. Not only does simply calling someone ignorant make their ignorance a fact, it by definition invalidates everything else they say.
Well, is vitamin C, Absorbic acid? Yes, it is, yet he claims that it isn't, and then he gives links that prove that absorbic acid is Vitamin C, yet he states that they prove the opposite, which is obviously untrue.
It is called ignorance, so, it is a factual statement that he is ignorant.
Not an attack, just a statement of fact.