The initial interview pass rate doesn't not relate to the number of open positions. It is how many people they are willing to try and find open positions for. Not getting a final offer from a company does not affect the rate of passing the Technical Interview. But I do agree that the on site success rates are affected by number of candidates per position.
There are more byas. The test difficulty is different per language, the years of experience, etc. You cannot extract any conclusions from this article.
