It must be misinformation week.
The whole world generally knows that a newbie trainee should very easily be able to gain muscle, lose fat and even do that on whatever diet they were regularly eating... for a short while.
Now, there might be some special cases out there, but please, don't be pulling strange special cases out of your ass and claiming it is normality.
Nutrition is pretty extremely important, in that you don't eat, you die. If you never lift again, you might be small, but you'll live (if you are eating).
Now, if you want to tie it, the question, to making gains, you need training stimulus and appropriate food in appropriate quantities. Except for untrained newbies, one or the other won't work.
It's not an or issue. Worrying about it in this way is apparently going to do nothing but have wild claims waved around.
[edit: as for the original poster, I expect the coaches simply assume the reader knows enough to eat appropriately when doing the programs in question.]