shrooms in my grow bags

I was checking things out yesterday and stumbled across a few really small mushrooms...they look kind of purple like cubensis.but are real small like fingernail size.
At first I was furious because I bought sterile soil.But then I thought about it and it should accually be a good thing(Micro wise)Shrooms live of oxegen and give of CO2...the opposite of MJ.So they help with a small amount of CO2.Also some people buy shrooms to put in there soil,so.
Once the canapy covers the soil I don't think they'll grow anymore.
What do you guys think...ever expirienced this before. :pimp:
It was only like five little ones and most were in one bag.