I'm not sure that's what's going on. The 'reset' part could be an adaptation to sickness in general. You'll notice that sick animals won’t move, won't eat and won't even drink, so reseting your immune system when you're unable to feed might be a good idea, as a common reason for not being able to feed is that you're too sick to look for food.
You'll also notice that yourself when you are accutely ill you are not hungry. I think it’s your body telling you that it has other shit to do right now than digesting stuff, which extremely costly and mobilizing a lot of ressources of your immune system. I believe the idea is a bit like that, your body can’t do everything at the same time, not digesting both signal a problem and free ressources for your body to sort the immune system.
If you look into actual science regarding fasting, a lot of weird shit is happening, especialy to the immune system, so when dealing with random weird health issue, it’s a cheap and safe thing to try...
Oh, also fasting is not starving. Starving is very very bad.