Facebook hires low quality engineers.

Not saying they do (not the poster you responded to) but why would you assume they wouldn't hire low quality engineers? No recruitment/HR/filtering process is perfect, no candidates are perfect, no hiring decision is perfect.

There seems to be an assumption that the big tech firms are inherently better at picking the better 'engineers'. Having experienced a lot of what they produce (not specifically Facebook, but Apple, Microsoft, Google, etc) I'm inclined to assume the opposite personally.

The guy from facebook was not en engineer but a developper advocate. I'd say this is VERY different.