And… he’s almost right!
The two manuscripts preserving the First Redaction in its entire, called the Book of Leinster (L) (c. 1150) and the Book of Fermoy (F) (1373), differ in wording and material, with F providing additional, probably interpolated, details. Here is how they present the story of the “UFO” invasion, in the translation of R. A. Stewart Macalister:
306 (L). So that they were the Tuatha de Danann who came to Ireland.
306 (F). Thereafter the Tuatha de Danann came into Ireland.
Their origin is uncertain, whether they were of demons or of men; but it is said they were of the progeny of Beothach s[on of] Iarbonel the Giant (sic).
306 (L). In this wise they came, in dark clouds. They landed on the mountains of Conmaicne Rein in Connachta and they brought a darkness over the sun for three days and three nights.
306 (F). In this wise they came, without vessels or barks, in dark clouds over the air, by the might of druidry, and they landed on a mountain of Conmaicne Rein in Connachta: Thereafter the Tuatha De Danann brought a darkness over the sun, for three days and three nights.
307. They demanded battle or kingship of the Fir Bolg. A battle was fought between them, to wit the first battle of Mag Tuired, (L) in which a hundred thousand of the Fir Bolg fell. Thereafter they (the Tuatha De Danann) took the kingship of Ireland. Those are the Tuath Dea — gods were their men of arts, non-gods their husbandmen. They knew the incantations of druids, and charioteers, and trappers, and cupbearers.
Another company says that the Tuatha De Danann came in a sea-expedition, and that they burnt their ships thereafter. It was owing to the fog of smoke that rose from them as they were burning that others have said that they came in a fog of smoke. Not so, however: for these are the two reasons why they burnt their ships: that the Fomoraig should not find them, to rob them of them; and that they themselves should have no way of escape from Ireland, even though they should suffer rout before the Fir Bolg.
This is all suggestive, but how do we know that they weren’t ancient aliens? If you expect to take the text literally, it becomes very easy. A few lines earlier, in 304 (L & F) and 305 (F), the poem states that the Tuatha De Danann learned science and magic from the Druids and scholars of four (human) cities! Also, their leader in section 310 and thereafter is Nuada, the king that Ancient Aliens told us only weeks ago was a human the aliens gave a bionic arm. Actually, though, they probably did originate as gods in mythology, before rationalization, since Nuada is undoubtedly Nodens, the great god.
As for the darkness, it isn’t the result of great ships as Childress implies; instead, it is a smoke screen, just like the one Athena uses to cloak Odysseus in the Odyssey and the one that hides Jason’s approach to Colchis in the Argonautica. Divine, yes; alien, not according to the text. And at any rate, a cloud is not a ship or a spacecraft. To make it so, you have to allow for symbolism, which negates the idea of taking the description literally.
Naturally, ancient astronaut theorists have made this into a Sitchin-inspired racist nightmare. According to online ancient astronaut claims like this one posted less than two weeks ago, the Tuatha De Danann were the Anunnaki from some Sitchinite fantasy, and they first settled in Ireland in search of (of course) gold. There, these writers claim, the Tuatha De Danann founded the homeland of the Aryan race, making Ireland both the font of human civilization and the home of the purest white people in the world.