Mushrooms in my Plant's soil, GOOD OR BAD?

I noticed that over the course of today some mushrooms sprouted in a plants soil I just transplanted about a week ago. I don't think the soils dirt is that damp, I try to prevent overwatering. However, it is FULL of roots from a past plant that was harvested. I just kinda mixed the old plant's dirt with some new dirt to kinda save money. Well anywho, so yea, I figure the roots are decomposing and causing mushrooms to form? But where would the spore come from though? I've heard a lot of people getting mushrooms in there miracle grow mix and such, so might it be the miracle grow mix?

Also what kind of mushrooms are those? does anyone kno?

No idea of the kind.. They are the fruiting bodies of the fungus living in the soil doing its job.