that's really strange. i've been in ketosis before, but assumed i'd be lactose intolerant whether or not in ketosis.
i'm severely lactose intolerant in that even lactaid milk will give me gas (that is supposed to be lactose free). However, strangely, FULL FAT milk barely gives me gas, whereas nonfat gives me incredible gas.
cheese does not give me gas, nor does yogurt, cottage cheese, or any of the cultured products.
so with that said, I came to the conclusion that I am lactose intolerant when I have non-cultured dairy without any fat. On a keto diet i'm assuming you have plenty of fats so that may be one possibility it helps dampen the effect of the lactose perhaps by slowing it down and giving the gut a chance to process it.