*white flag*
He was the Lord of the Mearas (being direct descendant of the first of them), the Mearas are the noblest and proudest of all horses, hence he was somehow also lord of all horses ("mearas" is also just an other word for horses, but in LoTR it was only used for the descendants of Félaróf), though horses - unlike carnivores - don't have lords, their system is based on equality, they have leaders from time to time in their groups, but no "lords"
😛