Aww geeze, not to be rude but don't you think such a video would be a bit obnoxiously inconsiderate? I mean the first Touhou exposure is usually as a result of randomly bumping into the related fan works, as either a direct or indirect result of the fandom of something else. It's not like Touhou is famous to the point where you'd have to live on Mars to avoid it. In fact, I'd say it's really just a cult classic at best.
The conclusion that it might be from an anime isn't even that far fetched either, considering that the overwhelming majority of its fanworks are anime styled, suggesting such an origin source. To be completely fair, most people find out about something like this from a more informative sources, such as advertisements, informative articles or through friends for a few examples. Pictures and fan animations don't really inform one of much and the doujin manga could be misleading. Even I.a.M.P. and S.W.R.'s sprites follow the stylistic enough to imagine there might be an underlying source that isn't a game. Consider Melty Blood's own origins with the visual novel Tsukihime and the considerable number of custom made MUGEN characters for a moment.
By asking the question they're already admitting they don't know where its from and would like to enlighten themselves as to the origin. The annoyed shouting out of what Touhou isn't doesn't help them find out what it is in the least. Politely answering the question asked by saying something like "X is from the Touhou series of games." on the other hand does both. I agree with some of the others; the mistake is completely one-hundred percent understandable. This is why I think what basically amounts to a blatant "You are wrong!" video would be rude. In fact I think it would make the whole Touhou fan community, worldwide, look like a bunch of jerks to be quite frank.
Oh, by the way, before you even think it; no, I never asked the question as phrased. I mostly lurked around places and learned about it through osmosis, though I do recall a friend of mine telling details me about the games themselves ages ago. It was so far into the past that the details are kinda sketchy for me.