Note that the mushroom in question has been growing just below the surface for some time. The part we are used to thinking of as a mushroom is, on many species,

Note that the mushroom in question has been growing just below the surface for some time. The part we are used to thinking of as a mushroom is, on many species, something like an inflatable flower that is used to release their spores. It is built just below ground over a long time, then inflated at the right moment (rains), and then abandoned while the below-ground main body starts working up the energy to do it all again.