Here[0] is a toy model experiment to demonstrate that neither Dark Matter nor MOND are necessary to explain spiral galaxy rotation curves, which coincidentally is the original purpose Dark Matter was postulated to explain. Dark Matter has since been fingered to explain other phenomena since, but it is not commonly known or accepted that galaxy rotation curves no longer needs Dark Matter (or MOND, for that matter).
Tl;dr Dark matter model simulation can't explain bullet cluster, and MOND can.
> Either way, the Bullet Cluster remained a stunningly unlikely event to happen in the theory of particle dark matter. It was, in contrast, easy to accommodate in theories of modified gravity, in which collisions with high relative velocity occur much more frequently.
The answer is most likely MOND + dark matter.