In addition to this
@Sabathius42 the sidebar in the PHB has this line "Raw magic is the stuff of creation, the mute and mindless will of existence,
permeating every bit of matter and present in every manifestation of energy throughout the multiverse. "
If we take this to be literal, then magic exists in the kinetic energy of swinging an axe to chop down a tree, or in the electrical energy needed for your heart to beat or your brain to function.
This makes "psionics are foreign to magic" mean they would have to be foreign to existence itself, which just does not work on many levels (unless you count Far Realms and make it solely based there, except even the Far Realms uses magic)