My hairy green mushrooms do that when I target feed them. I have a few that are over 4" diameter. They split every 2 or 3 months. I have given away a dozen or more in the last year. Started out with 2 the size of a dime. Still got about 10 of them the size of your fist. I'll be trying to sell a few of them soon.
My purple mushrooms, superman mushrooms and green stripe mushrooms won't eat a thing. But the hairy green mushrooms will eat daily if I would feed them. I usually only feed them once a week though.