They have their checklists and everything, it's not an unusual case when the plane goes to a runway and stops for a few seconds. Again, as an ATC, if you need a passenger plane to get out as fast as possible - be clear about it or don't clear them to the runway. It was also a Fedex pilot who figured what's about to happen by themselves.
Yes. The controller should have said "no delay" along with the takeoff clearance, but also given the extremely poor visibility (they couldn't even see 1/4 of the way down the runway), it shouldn't be surprising when a plane takes a few seconds longer on the runway to get situated and double check a few things.
