Haven't you people ever taken the bus?
It is obvious that this guy probably usually takes transit some of his trip, walking the gaps when the system doesn't work. (Missed transfers, busses offline, etc.)
In terms of "21 miles per day" that is just CNN counting his miles the way Letsrunners count theirs:
"Well, USUALLY I PLAN to run 10 miles every weekday. I don't most weeks because of work or something else, but I COULD."
"I COULD easily do a medium long-run 15-miler on Wednesdays. SOMETIMES I do. So lets say I do 55 miles Monday-Friday."
"MOST weekends I do a long run, SOMETIMES up to 23 miles."
"USUALLY I take the other day off but I COULD do another 10-miler."
"So yeah, I run 88.00 miles per week."