It's worth noting that in the history of tulpamancy, the metaphysical school of thought greatly predates psychological ideas. This is something that's kinda lost in recent years, and it's also why the slogan/motto of tulpa.info is "For Science!"
Pleeb, Lumi, or anyone who's been around for that general amount of time could probably give a much better history lesson- I've only been around since late 2018, and this is stuff I just learned FROM people like Pleeb and Lumi and other oldfrens.
Metaphysics, in this usage, also doesn't just mean "philosophy of reality." Not to mess with a dead horse topic, but Zen, and Shake in the past, and probably Proxi too, and others from even prior, sometimes use #metaphysics to shill their metaphysic philosophy systems. This IS the right place for that, but ORIGINALLY the intentions of #metaphysics was really to contain MAGICAL discussion, but the community saying "my tulpa is a magical soul entity" really didn't exactly want to be called wizards or anything like that- and the discussion was always more about "What is real, anyway?" and that's how the term "metaphysical" became used for the more magical and older lines of tulpamancy.
Metaphysics is cordoned off from the rest of the forum/IRC because people of the metaphysical (read: magical) school of thought were shitting up discussions by bringing their magical beliefs into them. "Are tulpas people?" "Yes because they have souls." That's the type of person who the metaphysics side is for- to prevent the discussion from being derailed left and right by "I don't believe your religion is true."
It makes it weird when #metaphysics is full of atheists mostly nowadays lol.