In Detroit, biking is doable at least during the 7-8 months of the year with no snow. The guy probably has access to secure locking facilities at home and work as bryanlarsen pointed out. He is paid $84.40 per day at his hourly rate of $10.55/hour so he can definitely afford a working used bike starting around $50.
I bike to and back from work daily 14 mile round trip using a cheap 2nd hand city bicycle. Snow and cold only makes it more fun.
Of course, I am lucky that I am doing it by a choice and could take the bus or drive my car.
For me, there's some sort of qualitative difference in a bike ride that goes over something like 10 miles, so I can see why it isn't a first thought for a 23 mile trip.
I can't possibly fathom why your first thought to travel 23 miles would be to walk? Biking is OBVIOUSLY so much faster, easier, less straining, etc.
He walks about 3.5 miles, takes a bus to the edge of its service area, and then walks another 7 miles to the job.
"Detroiter James Robertson, 56, walks about 21 miles a day"
So he would only have to bike 21 miles per day.