As someone who works out regularly but never cycles, this seems difficult to believe. Surely the cardiovascular benefits outweigh any negatives from "muscle shortening" (first I've heard of this) compared to no activity.
Unless your point is "some types of exercise are better than cycling" in which case, sure.
Fact - cycling creates short leg muscles, hamstrings in particular. For those of us who have tight hamstrings, which is most males (according to my subjective, biased observations), this is not good. Creates back problems later on.
I agree that some cycling is better than no activity. But I would say that going to a hooker every night is also better for you health wise than staying in and watching tv, as long as you wear at least 2 condoms.
Keep it up champ!