NO he has not cured his leaky gut! Just look at his diet. Eating only Bananas. I love bananas, I have about 8 Kg of them in my home but I do not live on them. A person cannot live on fruit alone because the body needs protein to function otherwise the body begins to release large amounts of cortisol in order to cannibalize/break down muscle to acquire the needed amino acids. For leaky gut sufferers, cortisol works against the body because it increases saliva production which you might of noticed increases when you eat. Nasal mucus also increases, ie you might get a runny/snotty nose. Without a regular supply of amino acids the body cannot produce it's detox and anti oxidant glutathione enzyme.
MSM supplies methyl groups which are important to the body and in many people can be deficient. I supplement with MSM myself for the methyl groups it provides. It is believed to increase glutathione production, although I am not certain that it actually does this. MSM does supply sulphur which can be a problem, molybdenum can be helpful.
L-Glutamine will not fix leaky gut, this is a commonly recommended fix which does not work. The digestive system uses it but that does not mean that it will fix leaky gut because leaky gut it caused by a bacterial infection. An infection which is extremely difficult to beat. These bacteria are a social infection and they can be passed through families by social contact. That is why his kid also got it from him. I have seen evidence for this in many cases, parents and their children infecting one another and each having reactions to foods.
Leaky gut does adversely affect methylation which is why supplementing with methyl groups can be helpful.
Without destroying the bacterial infection, which likes to cohabit with Candida as gram negative bacteria are compatible with Candida, you will never be free of it. They have the first choice of nutrients, take what they want and leave you with what they do not need. Weaken your body, liver and immune systems and make you feel like shit.