It is not about the direct patent licensing for the ARM architecture, but all of the other patents around ARM.
Companies like Qualcomm, Samsung, Broadcom, and Nvidia are all actively developing around the ARM platform, and that means a rise in patents related to that architecture that are not part of the ARM licensing deal that Apple had. Apple have shown that their designs are years ahead of their competitors in *some* areas, but hey still have to rely on patent encumbered technology for others areas. Apple are very protective of thier own intellecttual property, and they have repeatedly shown that they don't like paying others for their IP (see Apple vs Qualcomm). If they can't own the IP, then they will try to work around it, even if it costs them tens or hundreds of millions. Would it make sense, with their size and cash holdings, to invest in an entirely new architecture where they can own all the IP for anything that was not free?
With the M1, Apple have signalled they have gone all-in on the ARM architechture. This process would have begun long before the Nvidia/Softbank deal. Softbank did approach Apple to offer them ARM, but Apple would have rightly concluded that they would never have gotten that deal past the FTC or EU (they already have issues being seen as anti-competitive). Is it possible Apple could see the relationship with Nvidia-ARM as being a rocky one? Could they be quietly hedging their bet long term (ie. 10-15 years away)?
The RISC-V ISA is free and open. Unlike many free software licenses, the permissive license for RISC-V does not require manufacturers to disclose chip designs. With RISC-V Apple could have a completely proprietary chip and, as long as it maintains a base compliance with the ISA, it can still be a legal RISC-V implementation. Changes in chip architecture are nothing new for Apple and, while it is still in progress, the shift to ARM on their Mac lines seems to be going well. We now know Apple had macOS running on ARM long before the switch from Intel. We know they had OS X running on Intel long before the switch from PowerPC. We know they had Mac OS runnign on PowerPC long before the switch from Motorola 68k. Why should it be different now?
Or... we are reading a lot into a single hiring, and this could be for something completely different.