In this case though, the new driver has the same license as the project it was based on and explicitly credits the original project

  ISC License
  
  Copyright (c) 2010-2022 Broadcom Corporation
  Copyright (c) brcmfmac-freebsd contributors
  
  Based on the Linux brcmfmac driver.

This surprised me - but sure enough, they're right. The linux brcmfmac driver is ISC licensed:

https://github.com/torvalds/linux/blob/master/drivers/net/wi...

// SPDX-License-Identifier: ISC