Here’s a discussion with Ven. Sujato on blamelessness Self-immolation is not an authentic Buddhist practice - #10 by sujato
There’s also other interpretations by other monks, I remember reading Ven Dhammanando’s take several years ago, but it’s been a while.
My understanding is that there was no 3 poisons involved in the act, so not even “neutral” kamma is involved. If my memory serves me right, neutral kamma is still conditioned/caused by ignorance.