Nonsense imo.
The bad smell being a sign of toxicity is largely not true. Bad smell is a result of certain fats or sulpher compounds. Hard boiled eggs along with something that produces a good quantity of gas like bran fiber will prove this true. Cabbage is another example of a sulphery food that is going to add to flatus stink.
Over eating is a major cause of gas, as is anything that is not well digested. Fiber is by definition indigestable and high fiber foods are common causes of gas. Eating more slowly sometimes helps one have less gas. Chewing ones food fully can help. Constipation is a common cause of gas. Most people have some foods that have to be done in small quantities or not at all, or they suffer the consequences.
In ayurvedic medicine extreme gasiness, constipation, and being mentally spacey are considered a sign of a vata crisis, in case that system interests you at all. Exercise often speeds up digestion & elimination some and can result in less gas for some people.