The header does nothing. As the article says, the author sent the header in every request, made a total of 35M requests, and thus gained a reason to use 35M hot dogs in the article title.
Correct. Maybe it blows my credibility out of the water and I'll be shamed for life, who knows
Have you heard of "hotdog eating contests"? Or any other kind of eating contest? The joke is that he's having the two servers compete in "eating hotdogs" because the requests have a hotdog header. I think, anyway.