This isn’t unique to him, of course. Sir James George Frazer wrote The Golden Bough essentially to prove that Christ was just another dying-and-rising ancient vegetation god and Christianity just another mystery religion. But he and his wife excised all important references to Christ and the Crucifixion that would call the truth of Christianity into question from the 1922 one-volume popular edition of the 12-volume work to avoid offending religious sensibilities. All that remained were some wishy-washy statements about the "coincidences" that were "too close and too numerous to be accidental," without seriously questioning whether Christ was the literal son of God. Frazer, like von Däniken, also claimed that he had made no changes to his views despite the clear (and published) evidence to the contrary.
It’s unusual to see this happen and then have the author lie about it and immediately adopt a completely contradictory position to hock more books. But it happens. Ask J. G. Frazer.