Mankar Camoran as far as we know is an Altmer, yet he has racial attributes of Nords and bretons as well as Altmer. Not only that but he can wear the Amulet of Kings, how is that possible? Only those with Septim blood can and he is the son of Camoran Usurper. But his mother was a bosmer and the race of a child is carried by the mother (see-the grey prince) so he should be a bosmer but he's not! His paradise looks like a pre-alessian cyrodiil. Cyrodiil (espesially around the imperial city) is reffered to be a "jungle" and his palace is likely the only time in the game where we can see a non-ruined ayleid building.
I think that Mankar is a reencarnated Ayleid. I think that somehow ayleid magic made his mothers child an ayleid one. I remember reading about ayleid revenge at one point. It had something to do with the shape of imperial city. So this is my theory. What do you lore-masters believe?
Or he's a "plastic Ayleid". Somebody who isn't actually anything of the kind but has adopted, for his own purposes, some reconstruction of Ayleid culture.
As to the Amulet of Kings, that is either superstition, as the Septim bloodline has been in tatters for a couple centuries already and some distinctly non-Septim Emperors have ruled long and successfully, or more likely a case of "Septim is as Septim does": it's the soul of a ruler, not the blood of old Tiber, that makes the wearer. And even though he's as loopy as old mad Pelagius, he's of a royal line.
The problem with making him a Bosmer in game is that a runty Mankar Camoran would be even more risible.