If they have an architecture license, they can make their own implementations of the ISA.
Certainly, they may choose to derive their implementations from ARM's designs (or use them wholesale), but the license allows them to make their own.
That said, in the mobile space, AIUI only Apple and ARM are nowadays developing their own implementations. In the HPC space, there are others (Fujitsu, Marvell, etc).
(ARM also sells more limited licenses which only allow their cores to be used.)
Certainly, they may choose to derive their implementations from ARM's designs (or use them wholesale), but the license allows them to make their own.
That said, in the mobile space, AIUI only Apple and ARM are nowadays developing their own implementations. In the HPC space, there are others (Fujitsu, Marvell, etc).
(ARM also sells more limited licenses which only allow their cores to be used.)