Unfortunately I can't edit the previous comment anymore but you're right. Originally I was under the assumption that the conjecture that the propellant valve fa

Unfortunately I can't edit the previous comment anymore but you're right. Originally I was under the assumption that the conjecture that the propellant valve failed or started leaking upstream from it was correct. However, it appears that the entire vehicle exploded before the SuperDraco test even started. Since it wasn't just leaking out of a damaged engine, my assumptions about roughly complete mixing were wrong. There's very little chance that there wasn't a decent amount of MMH released as well.