It's a mixture of a lot of things! The main factors are moisture/humidity and the temp difference between the inside of the lens and the outside conditions. Inevitably all 'traditional' goggles will fog because even the best anti fog coatings will be overwhelmed at some stage - especically if you sweat and it's cold outside. The newest ones have built in fans and even a heated lens. This combination solves the problem!
No it doesn't. It helps.