I was in Newark that day.
There were over 400 road traffic accidents, and at least 2 bridges closed due to accidents.
It took one person in my office 6 hours to drive 7 miles, and on the 5 min walk from my office to my hotel i saw 2 separate car crashes.
While its not great being held on the tarmac for so long. had you been let off, you probably would have been stranded in the terminal as very little was running and traffic was not moving.