Sex between the Races Lore?

[Enkidoh]

Miqo'te hail from Meracydia (mentioned on 2.5) alongside centaurs, an unnamed tree-like race and the Bahamut and Tiamat brood. The "Winded-up Mithra minion" states that the Mithra are supposedly the ancient ancestors of the Miqo'te

The miqo'te coming from the southern islands is an old bit of 1.0 lore that is deliberately vague so take it with a grain of salt (the Dunesfolk lalafell and the ACN class were also supposedly from there as well).

As for the wind-up mithra, that is merely a fanservice reference that is actually a meta one - the original FFXIV races really were created game-development wise based on FFXI's races like the mithra as FFXIV 1.0 originally was planned early in it's development to be FFXI's literal successor, and that then FFXI players would be expected to be moved into the new game with their existing character data intact, hence the character races needed to be similar.

Not surprisingly FFXIV's original producer Hiromichi Tanaka (who was also FFXI's original producer) quickly realized this concept was going to be completely and totally unworkable so that idea was scrapped and FFXI retained as a seperate game, with FFXIV 1.0 considered a spiritual rather than a literal sucessor to FFXI, and the similar races were retained as merely a means of attracting FFXI players into the new game. So the wind up mithra, elvaan and tarutaru minions jokingly refer to this in their flavour text about being "supposed ancestors" of the miqo'te, elezen and lalafell respectively, because they are, from a meta, rather than literal lore point-of-view.

Also the Allagan automata that are still active on Azys Lla refer to the player character's race as is, meaning the FFXIV races existed as they are now at least as early as the Third Astral Era, if not earlier, which makes the descriptions of those minions even more tongue-in-cheek and not to be taken seriously.