If you ever dabbled with dmt, you know good and well the least weird thing you could possibly see is a giant octopus coming out of a pyramid.
I once smoked dmt wound up in a 27 yo females head (I'm male btw and 35 at the time) experienced every memory she had from kindergarten to job interviews and at one point she recognized my presence in her mind and we both had this incredibly weird moment and she began to show me some of her more personal feelings and we played in her mind like this for a while until I became the ingredients of emotion or the pieces that make up feelings and exited her body as a tear and came to balling on my couch...and that is the least weird dmt trip I've had.
I'm sure you could hallucinate a giant octopus coming out of the Great Pyramid.
I don't think the Ancient Egyptians, in general, could because most of them didn't live near an ocean and it's not like an octopus is easy to keep fresh when you're taking seafood down the Nile to trade.
Also, they knew that the pyramid was a tomb for a pharaoh. It's not like that was a secret. It's never been a secret. People just want there to be a secret involved. I guess because it's a funny shape? I don't know.