So more than once I have heard that biking will help your running but running does NOT help your biking? Why is that? Do you think that is true?

So the past year I have primarialy ran, with intermittent biking. I am not fast at either but always had good endurance. So beginning of Sept. I got back on the bike and was able to quickly ramp up my mileage and kept up with the gals I ride with, they had been building in a reasonable manor. Like I said we are not speedy but go for distance. So I think the running kept me a good fitness & endurance base. So what does it mean that running will not help your biking?

Just wondering what everyone else thought or experienced with the two disciplines.

K