Yes, the potting mix you used likely was contaminated with mushroom spores. It is hard to know how extensive it is. But before you do anything radical, like changing the soil, there are a few things you can try.
First, gently scoop each mushroom out so you get the roots (called mycelium) as well as the mushroom itself. If you just pull it out, the fragile mycelium will remain.
Next, remove and discard any soil you added to the surface of the original rootball when you repotted.
Finally, allow the soil to dry as much as possible before you add any water. Mushrooms require constant dampness to survive. Warmth and sunlight will also deter them.
You may not want to use that potting mix again. Look carefully at the ingredient list on packaged potting mixes. It should list only peat moss, coir, perlite, and vermiculite. No compost, soil, bark or other ingredients that are not sterile and may harbor fungi and gnat larvae.
