I think it was purging leftover hypergolic fuel, which is used to ignite the engines. Or, maybe the engine sensed the engine was abnormal (because of low fuel), so it tried to re-ignite.
TEA-TEB is not used on Starship. What you saw was an oxygen rich burn due to the low pressures in the header tank, the engine was eating itself and burning copper in the process. Copper burns green.
Yo what's going on here? Is this some sort of misinformation campaign? To what end?? There's been a number of comments making this claim even though there's no reason to suggest this was the case.
Definitely not misinformation, just misinformed armchair enthusiasts. SpaceX did the hard thing using spark ignition which goes against the industry norms. Even the everyday astronaut YouTube guy said tea tab on his stream and he’s a space nerd.