It'd be helpful if you're gonna post something that sounds like pseudoscience to post a source with it. With all of the studies covering inane things, someone has got to have studied this.
The switch to anaerobic glucose metabolism is part of the evolution of cancer as it progresses. This is because oxygen diffusion into a solid tumour is a limiting factor upon its growth. Cells which switch off aerobic metabolism will be selected for, since only they will survive and proliferate in an oxygen-free environment. You'll find this in most cancer textbooks. It's not new; I was taught this in undergraduate lectures two decades back. This switch is actually one of the key control points which holds a brake on the progression of a cancer past ~1mm in size, which is basically the limit of passive oxygen diffusion into the mass.
It's fairly logical to keep glucose levels minimal to reduce the growth of this type of tumour, and removing sugar from the diet is a simple and effective way to do so. A diet which is based upon fats will do this, since fats can be converted to the minimal levels of glucose the body needs via beta-oxidation. This will reduce the metabolites available to the tumour significantly, compared with the huge spikes you get when you absorb it directly from the gut.
https://scienceblog.cancerresearchuk.org/2017/05/15/sugar-an...
Also note that the link does not say, at all, that dietary restriction of simple carbohydrates is ineffective. What it does say, is that dietary restriction should be discouraged in case it causes malnutrition and/or weight loss, which can be counterproductive with effective treatment which itself can also cause weight loss. Which are completely fair points to make for safe general advice to the public; nothing here is black and white, and making definitive statements one way or the other would be both impossible and irresponsible.
So in some situations it may well be counterproductive. However, that is not saying that there are no situations in which it can be effective. Cancers are incredibly diverse, each type evolving in a unique way with different courses of progression. In some cases, it may well be the case that such restrictions can help.
My partner actually researches prostate cancer and i asked her about it and basically her answer is that its complicated. In her research, she found that cancer cells in the prostate are able to find other sources of energy so cutting glucose might not help. From what I understood (not a biologist) it basically depends on tissue and mutations.