I favor the theory that Strange knew good and well that there's such a thing as chaos magic having wielded it himself, but–given that he was dealing with a horde of mouth-breathing Avengers second stringers yammering at each other in Bendispeak–opted not to go into a detailed metaphorical explanation about styles of magic and the dangers of misusing same. Instead, he went for the terse, grouchily-delivered untruth that made people shut up and let an expert deal with the situation.