Unassisted bicycles that are ridden faster than that certainly are bicycles. Which points out a huge problem with certain approaches to bike infrastructure: if you force everybody down to the speed of the slowest ones (usually small children) because there are no opportunities for safe passing, then bikes can't compete with cars for any distance beyond walking. having to go 12 km/h when you would do 30 is worse for your commute duration than having to go 25 when you would go 50.
It's not a problem in Copenhagen. Most bike paths are wide enough to allow overtaking, and even the fastest cyclists are respectful enough of small children to slow down as they pass. (Many fast cyclists will be parents, after all.)
