I have to admit that I've never really thought about it. But, my impression is that consumption is an act within FTT.

When I hear full toilet training, I think of both golden and brown both on the body and consuming with it all being part of training by a Domme. That is more comprehensive than just consuming. Although I do think that a lot of people just use them interchangeably because there isn't a specific definition of the terms that everyone agrees on.