Spontaneous, "starterless" sourdough

I have been experimenting with very long, slow rise times i.e. 12 hour autolyse then add very small amount of starter (flour in starter weighs 2% of weight of all the rest of the flour) and let rise another 8-12 hours. Then a couple stretch/folds to shape loaf. And hour or two more rise time and bake. Also baking at much lower temps to preserve nutrients and minimze acrylamide formation, 250-300 degrees for 1 1/2 to 2 hours bake time.

Just on a whim I did something different and got a surprise. I ground 25% teff 25% kamut and 50% einkorn. Added water to 72%. Formed it up and covered well and walked away. Now, about 48 hours later I checked and it has risen, a lot! Nearly doubled in size. Smells nice too. So I mushed it down (it is quite wet as I the long autolyse seems to reduce need for water) into a loaf pan and will bake it in an hour or two. I have not baked it yet so no idea what it will taste like but based on the rise and the aroma, should be excellent. Only issue might be that it has over risen. Time will tell.

My starter never left the fridge. For this loaf, it was apparently inherent in the grain in enough quantity to get a robust culture going in 2 days. I guess that shouldn't really be a surprise since that is how one usually starts a new starter, but this seemed to be quicker and more robust than anything I've done in the past.