I never had WLS but I know a lot of people who did, and this is the first I've ever heard of this milk only diet. In fact, I've heard that you must lose some weight prior to the surgery, but never just milk. But I googled this, and according to what I read, this is very common.
I too recommend that you check with the other facility and compare the recommendations of both.
"Whatever your goal, you can get there as long as you are willing to be honest with yourself about the preparation and the work involved."...Oprah Winfrey
Although no one can go back and make a brand new start, anyone can start from now and make a brand new ending...Carl Bard