I speak from experience because I have encountered such non-human intelligences myself in the 70-or-so sessions I have had with Ayahuasca and with smoked DMT. I have encountered them and I have learned from them. They have given me teachings. Now I am aware that materialist scientists will say these encounters are not "real" -- and those scientists might be right! -- nonetheless the non-human intelligences I have encountered, interacted with and learned from have seemed very real to me. I therefore have no doubt that they seemed very real to the shaman priests of ancient societies who also certainly explored deeply altered states of consciousness and who also therefore encountered such non-human intelligences -- the "ancient teachers of mankind" as I referred to them in the subtitle of my book "Supernatural". In this connection please note that shamans in the Amazon today are quite clear that even the knowledge of how to make Ayahuasca itself was taught to their ancestors by non-human spirit beings in the long ago, and that these spirit beings were encountered in the shamanistic trance state, not in an everyday, alert, problem-solving state of consciousness. Remember there are multiple ways known to shamans to get into the requisite trance state. Meditation as practised by Buddhist adepts would certainly be one of those techniques, but there are so many others. The Bushmen of the Kalahari encounter spirits after dancing for hours around a fire (the trance dance). And in the Amazon there are many other teacher plants as well as the two (selected and put together out of the 150,000 different plants and trees of the Amazon) that go into the Ayahuasca brew.
The implications of all this seem to me potentially to open up a much more fruitful line of enquiry than the simplistic materialistic notion you are advocating here (unless I misread you!) that our ancestors were contacted and taught by "aliens in the traditional sci-fi sense" (by which I presume you mean physical beings a bit like us, or perhaps very different from us, but nonetheless physical beings but with higher tech). The enquiry I prefer is into the multi-layered nature of reality, in all its dimensions, filled with sentience and mystery and linked by consciousness which is itself perhaps the greatest mystery of all. In my opinion the physical, nuts-and-bolts "traditional sci-fi" alien solution does not do justice to the vast and complex nature of the mystery we are confronted by and that our ancestors, also, were confronted by and described in their texts.
Warmest as ever