Then what is Dabura and the "Demon Realm"? O.oNo, demon is not a species in this series
Weren't there demons in dragon ball too? I think that was filler though...
But what if Toriyama never said anything at all about this? If Toriyama intended on Goku being an alien from the beginning, nothing changes. Was Goku even ever specifically labeled as anything else, be it alien, human, or whatever in any official source material before being declared a saiyan?Yes, it does matter if it's unintentional or not because intent is at the very crux of what a retcon is. A retcon is retroactively changing intent. Whether or not it goes hand-in-hand with what we know before has no affect on whether or not it's a retcon because fitting into the story is more of an in-universe concern while retcon concerns itself more with the out-of-universe, i.e., the author's intent. If Toriyama did not intend Goku to be an alien from the beginning, he was not writing Goku as an alien. If Toriyama was not writing him as an alien, Goku was not an alien. When Toriyama decided Goku was an alien, he became an alien, and, by consequence, he retroactively became an alien in all those previous stories where he was not. In-universe, that means he's always an alien. Out-of-universe, he only became an alien the moment Toriyama made it up. That's retcon.