At 80 people it might start being the time to question whether its really everyone else thats unskilled or your approach to evaluation is wrong. Asking a pop quiz of arbitrary tools / techniques that you happen to have remember really isn't a good way to evaluate if someone is a good developer. I am a good developer and I only just remember what clearfix is, I most certainly couldnt explain how it works.
It doesn't even sound like he interviewed the candidates at all. > Although I only had the chance to review their personal websites or github profiles and this might of course not be a full show-off of their knowledge, it assured my lately developed opinion on web developers. Apparently because people's personal projects weren't developed with accessibility in mind he concluded that developers don't know HTML/CSS.
>Many are not able to [...] to explain why and how a clearfix works, or what ARIA roles are for
I have only had the chance to review this blog post but this person doesn't seem to be able to explain simple arithmetic, describe the difference between something that is round vs square, or tell me what a spoon is used for.