A lot of time people will move to a new job for a more senior position than their current job. Being a Sr. Engineer at a Series A funded startup can be very different than being a Sr. Engineer at Facebook (not always, but often). I would expect a higher bar at a larger engineering organization.

If someone is effectively testing for these more difficult subject matters then it's quite possible that they themselves and other co-workers are competent in them (as they passed the same test).