HE IS! He totally is, as per chapter 6:
“The Swiss became as purple as a peony. He wore his elegant uniform, D’Artagnan was wrapped in a sort of gray cloak; the Swiss was six feet high, D’Artagnan was hardly more than five;”
That explains a lot, I would say: the short temper, the fact that he wants to duel everyone who looks at him funny. It makes a lot of sense for d’Arty to be tiny. And perpetually angry.
I once saw a review of the musketeers that referred to ‘the improbable heights of the main cast’ (and the level of dental hygiene which is also a good point) which is a fair point cause its 1630 and just over five foot is probably about average (okay still maybe a little shorter than average) from what they estimate from skeletons and military records and the like
fearlessstateofmind backup 