No, talk about wind direction is not immaterial when dealing with ash fall out....
I live in So. Cal I've seen it rain ash in a big way...For days at a time....And where it rains ash my friend, it's directly dependent upon wind direction.
You are comparing fire-generated ash to that of a volcano, which can produce pyroclastic flows that go where they want to go, and nothing can stop them except distance. Seriously, have you ever been to St. Helens? I have. The power unleashed there was stupendous, but it is a nothingburger compared to Yellowstone.
Are you basically saying that geologists mapping a contiguous formation of ashfall are wrong? That is nuts, you are engaging in speculation and they are mapping ground truth.