A friend of mine landed in Vancouver, cycled to Kamloops in a few days, rode the Rocky Mountain 1200 (I met him on that ride), in 3 days, then took 3 weeks to cycle from Kamloops, BC to Boston - pretty much all the way across North America, then took another 3 days to ride the Boston-Montreal-Boston. He covered 8000 kms in 5 weeks ... and rode the 1200Ks on a fixed gear and the rest of the time on a single speed.
I know a lot of other Randonneurs who could do similar things ... I've even got friends entering the RAAM (Race Across America - 5000+ kms in about 8 days).
I don't recognize the name of the guy in the link you posted (I thought he might be one of the Randonneurs I know), but I think it is entirely possible.
Take a look at the Links page on my website to see many of the long distance events out there, and the people completing those events.