Best i can tell it is complicated.

Sailfish is based of Mer, A community reimplementation of Maemo without the proprietary Nokia bits (power management being a key part), that was started before the merger. But adopted various Meego elements afterwards.

BTW, it was the Sailfish IRC channel that spawn the supposed Poettering death threat. It was actually a bad joke about using kickstarter to fund an assassin after the Sailfish teams latest late night session of fixing breakages that a updated systemd caused. yes, Sailfish use systemd. And they were also a early adopter, if not instigator, of Wayland.