Technically, the Crown owns the land. Everyone else owns an estate in this land. This distinction only really becomes important if you do something silly like die intestate (without a will) and without any heirs, in which case title reverts back to the Crown. Or if you find oil, gas or coal under your house in which case you don't get any of it. ;)
There's an argument that "real" in "real estate" doesn't mean "tangible", but comes from "royal" or "real" in Spanish, meaning the King ultimately owns all the land.
It would more likely come from French (in which "réal" meant "royal" in the past, see Montréal - Mount Royal) seeing how French influenced English legal terms and such.
This explanation makes more sense to me intuitively, as there is a lot of material stuff that is not "real estate", in fact majority of stuff that is material is not real estate.
This is one of the times I can say for sure that I know what I'm saying. A mix of improbable circumstances.
The funny thing about the link you share is that the two comments that offer the real answer are the least voted.
They explain why actions were called in rem (a demand related to possesions as opposed to in personam) and that real estate is refered to goods that you can't move, as opposed to furniture. Actually in Spanish real estate is "inmueble" while furniture is "mueble".
I think Hong Kong is also owned by the state...you can lease it for as long as 999 years. https://en.wikipedia.org/wiki/Government_rent_in_Hong_Kong but you do not own it. But in reality you own it and 999 years later you're related to half of the world (give or take :))
Let's not forget that for land in many countries, if a squatter uses your lad for xx years without being challenged, it is theirs. So it's recognized as different.
"With the exception of oil, gas, coal, gold and silver, the state does not own mineral rights in the UK. Generally minerals are held in private ownership, and information on mineral rights, where available, is held by the Land Registry together with details of land surface ownership."
