I think it has. Besides the dry yeast, I left it overnight without a top, to catch wild yeasts from the air.
It bubbles like sourdough. Smells right. Has the elastic, sticky texture. I'll give it a go before long.
I make different kinds of dough using yeast and when they're left to ferment, they have those same characteristics. But they're not sourdough, even though they taste and smell sour after a day or so.
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Some of my favorite breads, especially rye breads, start out with regular yeast, and are sour after a few days - not the same as a sourdough, but just as good, and easy to achieve repeatedly, starting from scratch.