As I recall grok said it was a misinterpretation of satellite pic.
As is typical, Grok will “evolve” as more info becomes available. Grok now says maybe intentional dumping, maybe a large spill. If these spills repeat, the answer will become more clear. It’s also possible it was done as a message, as this slick will end up on the shores of the GCC countries (my guess, not GROKs).
Bottom line is, there is no evidence either way at this point.