If not eating sugar could slow (all) cancers, then not eating at all would clearly cover that case, and should have slowed the lung cancer.
At the very least, his anecdote is convincing to me that it "starving the cancer" doesn't work with lung cancer.
In the more general sense though my first impression of the phrase "route energy through metabolic pathways that cancer is disadvantaged for" is that it sounds like random word salad.