Everything depends on the environment, sometimes you don't even have to keep up with the traffic, because that's almost non-existent
On winter mornings I could easily do 50-60km/h (31-37mph) along the road 811 (in Hungary), because at 6am the best unit to measure following distance was km. And I had to go that slow because it was already cold enough on the bike without going faster
Anyway, if I remember well, he always mentioned city riding, and not of the fast kind.