I’ve never quite heard of the ‘Ancient Alien’ hypothesis, especially not stated in such a way. I am familiar with the ‘Ancient Astronaut’ hypothesis which is quite popular and similar except for the ‘It was actually God part’ – That said, I would personally put both ideas in the realm of ‘possible’ but not very probable.
The main reason being Archeologists have a fairly good understanding of the emergence of intelligence and technology among humans and pre-human civilisations throughout history. We know about when humans first started developing tools and art and about when they started developing social cultures where these trades were passed down from generation to generation. There’s really no need to invoke the supernatural to explain these developments. So why do so? But more importantly, why do so BEFORE exploring and exhausting all possible ‘natural’ explanations first?
When you attempt to explain away an unknown with another unknown, you’ve explained absolutely nothing. You’re basically saying, “I can’t explain how this thing came about, so I guess it was caused by this other thing I also can’t explain.” — That’s not a really good explanation is it?
The second main reason would be that if a god came down to share ‘knowledge’ with early man… where’d all that knowledge go? Where was the knowledge that the Earth is round, that the universe is massive, that disease is caused by germs, etc. and so on? One would assume a god sharing knowledge would have access to these basic facts about the way things work. A better explanation would be that humans slowly developed this knowledge on their own, making major errors at times and getting things close to correct other times. Slowly building up the store of correct knowledge and discarding the incorrect ideas. Which pretty much sums the history various scientific disciplines have uncovered.