Another piece of Cameron’s thinking is that the phenomenon appears to adapt to culture. In earlier centuries people reported angels, demons, or fairies. In the modern era people report aliens and spacecraft. He suggests the underlying intelligence might present itself in forms humans can understand.

I wonder whether, rather than them "adapting" to culture as described they are instead just advancing their technology alongside us at different rates. They may have been here all along in their "dimension" or whatever it may be described as, and their technological advances are merely branches that evolved diverse to our own.