'Epidi' doesn't sound too much Gaelic at first hearing. something like 'ep(-os)' root? not 'ec' ('each': horse).
Concerning old ethnies descriptions by ancients, let's be sceptical a bit. But at IA it seems some continental Celtic tribes o sets of tribes migrated to Britains, rather in East, from Switzerland or SouthGermany periphery, and they had some 'alpine (short brachycephalic brunet types) with them, maybe by exogamy system of mating with women of previous pop's, if I remember well. And we cannot exclude totally ancient Neolithic pockets of dark people (but Neolithic 'Longbarrows' 'atlanto-mediter' people were not so short, in reality).