This would seem to imply that ancient Egyptian magic wasn't as constrained as Hermetic as to the Limit of the Soul. OTOH, it could just be a fairly comprehensive breakdown of Mentem magics too.
I can see pyramids as a way of granting the mystery of the Living Ghost to their occupants. It would certainly explain all the grave goods, and Ars Magica has already pretty much equated 'godhood' with gaining a Might Score.