The one meal thing comes from a Zohar in Parshas Mishpatim cited by the poskim in YD 89:
?? ?????, ??? ??? ????? ??? ????? ?????? ????, ?? ????? ??? ?? ??????? ???, ?????? ????? ?????? ???? ????? ??????, ???? ????? ??????, ?????? ?????
He talks about eating milk and meat in the same meal.
However, he does not indicate that he is talking about milk before meat or meat before milk. He may or may not have been.
Since we have Gemaras and Rishonim and a Shulchan Aruch which make no mention of an issur to eat milk before meat in the same meal, it makes sense from a halachic standpoint to either say the strict halacha is not in accordance with the Zohar, or better yet – that the Zohar was never disagreeing with the way we saw things until now, because he was simply talking about the case of meat before milk, not milk before meat.
Therefore, while one may certainly choose to be machmir, there is very solid halachic basis for not being makpid on separate meals for milk before meat.