Things don't need to be outright stated for it to be considered a retcon. Early Naruto was an established human/spiritual world, not an extra-terrestrial, sci-fi, moon people/parasite story.
In fact, not just early Naruto, pretty much the entire way through until the end. The sage of six paths was a completely unique entity, said to be a monk who was the first person to discover chakra. Kishimoto pulling an alien out of his ass and dropping a whole bunch of them is not just a 'lore reveal', it is completely rewriting the established lore and tone of the series.