What did I just make by accident?

I was making dough for pizzas, for my daughter's birthday party.  I was making enough for 6 crusts, so I had a larger bin full of the dry ingredients, and I managed to balance it poorly on the scale and ended up adding way too much water.  

I didn't want to throw out that much material, so I put it aside, covered.  It formed a sponge on top of a layer of liquid overnight.  It smells... not like a normal bread fermented with commercial yeast.  It's a little bit sharp, similar to sourdough starters I've made before. 

I suspect I managed to have some wild yeast sneak in.  I'm suspicious, cause I've never had it happen that easily.  I know that if a culture turns pink, there's an undesirable organism in there.  This didn't - was I really that lucky to get a sour culture going in a day?