It's pretty easy for me to figure out where DD learned most things, actually. Or it was, until she started reading independently. From the time she was a newborn, I talked to her about whatever we were doing. I narrated my life, and I'm sure that colors and numbers and body parts came out of my mouth. Shapes, not so much (and I'm also not sure that she knows more than the basic ones). What is a rhombus, anyway? LOL
As far as whether most preschoolers are taught, I think the answer is clearly yes. That's pretty much what preschool is all about, after all. Of course, that doesn't mean that they wouldn't pick it up on their own if they weren't taught. There are plenty of unschooled ND kids, and they learn without instruction perfectly well.
