It's true that Linux does this, although my impression is that FreeBSD and Solaris have comparatively stable ABIs. I think they usually keep the kernel ABI stable between minor patches, and change it with major releases. I've never futzed about with e.g. nvidia drivers on FBSD or Solaris, so I dunno.
Anyway, it was definitely just a weird mistake, I'm more intrigued about how varied the Illumos branches/distros are, since I had thought they were mostly just different userlands/package managers, when they seem to have different kernel patch sets and bugfixes...
I had a similar thought but on further consideration Linux does about the same. Linux freely breaks internal ABIs at will at least across versions; you can't use modules from Fedora on Debian in practice, if nothing else then because they aren't on the same exact minor version.
> The biggest question to me is why Helios is using the FUSE kernel module from OmniOS.
It was kinda unclear, but the impression I got was that they don't in general and this was a one-off mistake where someone compiled on the wrong machine by accident.