They can design their own ARM cores, they don't need to use ARM the organization's cores. Apple does that, which is why they have, arguably, the best SoCs out there. Laptop chips beating high end desktop x86 CPUs in single thread and multi thread, phone chip more or less matching or beating high end desktop x86 CPUs in short burst single thread (cooling being the limiting factor for anything else).

If Huawei does the same, future Matebooks might drive the likes of Dell and HP out of the laptop business.