I don't even know what this equates to in D3 specific IU measurement, but I'm guessing he either meant or you misheard 'international units (IU)' for miligrams (mg). Additionally, he's recommending, IMO, an overly conservative dose that is really not going to make a substantial difference in 25(OH)D in most people, but I'm glad he said 'at least,' and that he got the form of D correct.