How come mere water buffalo milk and lemon juice mixture turn into yogurt?
This is not yogurt per definition, you are making a fresh cheese. You can actually use other types of milk for such a cheese, but the mouthfeel and taste will be very different and won't be as similar to yogurt. 

There is a large class of acid-curdled cheeses, including paneer, tvorog, quark and many others. I don't know if yours has a specific name. I know that there are people who for some reason can't tell the difference in taste betwen quark and yogurt. But it is still cheese, even if it tastes similar to yogurt.