When i started playing forge on my own, I go on ghost cam to look on myself multiples of times. I gone back to spartan cam then turned into a forge ball then i died and i transformed back to a spartan after re-spawning then i go on ghost cam then looked at myself and i thought i was tripping or dreaming but i wasn’t.
Since viewing cinematics in Forge hows everyone as FOTUS, I think that’s the default armor in Forge. My theory is that when you die as a Spartan, the game checks your customization to see what you’re wearing, then spawns you with that. Since you don’t spawn as a Spartan when you die as a Monitor, I think the game doesn’t check your customization, because you just spawn as a Monitor. In most situations, the game doesn’t need to check your settings when you switch from Monitor to Spartan, so it only checks what your armor is set to, which would be the default, which is FOTUS for some reason.
Or it’s just a fun little easter egg to let people who don’t have FOTUS wear it for a little while.