I just think that those are just his cycling miles. You also need to factor in his runs. That's a lot of time.
Most triathletes do flat miles, which does not interest me. I will always make fun of their aerobars and call them flatlanders. Currently average 108 feet per mile of climbing this year, and if I did just flats, I'm guessing I could double my mileage count. Probably not 13K, but perhaps 10K. I also run, but only about 200 miles a year.