Pretty much everything is from systemd.
So I think ORAC is smarter about the framebuffer being used (not sure where tho Here I think).
Norns software is hardwired for a specific framebuffer (depending on which pi you have). On a pi3, the HDMI is always framebuffer 0. But, on the pi4, the framebuffer gets dynamically assigned, so with nothing plugged in, the OLED is fb0, but with HDMI plugged in, HDMI is fb0 and the OLED is fb1 (so norns goes to the HDMI)
Note - If someone has some bash and systemd skillz - please DM me