I don't disagree with the overall point, but the McDonalds analogy doesn't quite work.
By specifically going to McDonalds you are indeed showing them that you're shopping for a McDonalds Happy Meal, because that's all they've got to sell. But when you're searching for a given term on a site that indexes the entire internet, you're just looking for whatever's most relevant, regardless of where it's hosted.
If you'd wanted the search to only apply to YouTube, well, that's what direct youtube.com and the "site:" keyword are for.
By specifically going to McDonalds you are indeed showing them that you're shopping for a McDonalds Happy Meal, because that's all they've got to sell. But when you're searching for a given term on a site that indexes the entire internet, you're just looking for whatever's most relevant, regardless of where it's hosted.
If you'd wanted the search to only apply to YouTube, well, that's what direct youtube.com and the "site:" keyword are for.