Well, I finally found out how my mystery mushroom came to be.
I hosted a private studio tour for the students of the McGroarty Arts Center about 2 months ago and the organizer of the tour, Michelle, left her gift for me as a token of appreciation when she came to the house. She actually made the mushroom during the paper clay workshop I conducted over there, and I recalled seeing her working on it.
So, now, I can sleep at night knowing the souce of this adorable mushroom. It certainly was well hidden in my garden or I have to be more observant of things popping up. Maybe, I just have to do more yard work !!