No one else owns the freehold, you share it (and its responsibilities) with the other flat-owner.
The easiest way to think of freehold/leasehold is to consider the freeholder the owner of the builder - they own all the fabric of the building and flats within it. A leaseholder has bought the right to live in the flat (or let someone else live there) for the length of time left on the lease which is why a leaseholder has to ask the freeholder permission to make any modifications.
By dividing the freehold between the leaseholders - share of freehold - each leaseholder has an element of control over what happens to the building: its maintenance, modifications, improvements etc. But, that share isn't related just to the part of the building that you reside in, so you need a lease to lay out what you are allowed and not allowed to do within your own flat and where the shared responsibilities lie.
There will be a company that owns the freehold you and the other flatowner 'own' the company 50/50. Sometimes managing the company is outsourced sometimes freeloaders do it themselves (my preferred option). The company issues the leases therefore you set/own your own lease. It's the best scenario for a flat.