It would have been something closer to kefir, which processes at room temperature- yogurt needs to be kept around 100 degrees to work.
Kefir will separate into curds and whey if you let it ferment long enough.
Did a quick google search on the differences. Pretty much bacteria and temps. There is no way I would have consumed the contents of that milk jar on the counter on its own. Ugh. Bad enough when it was nearly solid cheese by the time it went into the pancakes!