Yes, as noted by Elon Musk on Twitter shortly after the RUD, they had noticed low pressure in the header tank during descent. This resulted in the Raptors after relighting quickly running out of propellant, leading to one Raptor flaming out and the other running 'engine-rich', as Scott Manley put it.
Basically the combustion process was eating its way back into the engine's structures, assisted by the hot temperature of the engine and the supply of oxygen feeding back into this. So yes, that green flame was literally the engine burning up, including copper or copper alloy-based elements.
Biting the hand that feeds IT
