Serfdom was on its last legs in England by this stage. I believe there were plenty of landowners who practiced the longbow but a majority would have been yeomen who were tenants of big solid farms, not themselves landowners. England was almost the first place to get rid of serfdom and a peasantry both, though the Netherlands may have it beat. Remember we’re on the verge of the Reformation. These are quite urbanized bourgeois societies by the 1400s.

"If you want to train a longbowman, start with his grandfather." Being a longbowman took extensive training and practice.

As far as I am aware, most longbowmen at the time were yeomen, a sort of middle class between the landed gentry and the serf class, where they owned their land and thus had the free time and energy to practice and hunt with a longbow.