They’re going to really get excited when they realise the crown estate is actually the whole of England and Wales (less the duchy of Cornwall iirc).

The bit they are talking about is the residual that hasn’t had a “freehold” tenancy granted to some other person.

You can’t hold land in England and Wales. The Crown owns it all. All you can hold is a heritable interest in land - an interest that returns to the Crown if you die Bono Vacantia.