both stacks were coded by broadcom(?) in the 90s, open sourced as apache license, abandoned, and recently maintained by a single RH engineer assigned 50% to it under the freedesktop org. who most change stuff so it work with wireplumber audio stuff. it got a 1.0 release recently because they fixed the new api, sill same codebase for the "actual dealing with bt radios"
i say both because most apple code is lifted from it.