Please don't quote me on this.
I think it's not a License question but they're taking a different approach. Linux binary compatibility has been around for a while now, at least longer than modern LX zones (I don't know about old Solaris lx zones).
There are some more subtle differences like the for BSD Linux emulation is a global setting and 'lx jails' are just jails w/ a Linux userland while branded zones are special kind of zones.
It does, I was a bit confused at first as well. It should be noted when project fifo says "lx jails" it does not mean LX branded zones from SmartOS. It means FreeBSD's native Linuxulator. Which has been in FreeBSD for.. many many years. It's a similar take on LX zones, but FreeBSD native. It does the same thing. Runs native Linux binaries.
Asking because last time I looked the FBSD stuff wasn't "really there". This would seem to still be the situation: "a true (albeit limited) ABI implementation is provided."
As soon as you see “syscall translation”, those are the magic words and they mean that the support is pretty complete. Sure there might be edge cases but if glibc can make a Linux syscall and get good data back, that’s it.
There are some more subtle differences like the for BSD Linux emulation is a global setting and 'lx jails' are just jails w/ a Linux userland while branded zones are special kind of zones.