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.
If I had started this a year ago I would be at goal today!
First Goal - 199 Onederland!
Second Goal - 180
Final Goal - 150