This is a good explanation, but there's a bit more to be said about MOND. MOND only argues that dark matter is unnecessary, it does not argue against the exist

This is a good explanation, but there's a bit more to be said about MOND. MOND only argues that dark matter is unnecessary, it does not argue against the existence of undetected matter. If you look at a galaxy, you can measure the amount of visible mass using star luminosity, and you can calculate the total mass of the galaxy under standard cosmology using orbits, radial velocities and so forth. Comparing the visible mass to the calculated mass reveals a huge discrepancy. Some of the undetected matter can be normal, baryonic matter, but there is to much missing matter for it all to be normal matter. So we postulate the existence of an unknown type of matter that interacts gravitationally but not by radiation (light). Using MOND, when you calculate the the mass of a galaxy and compare it to the visible mass, you still get a discrepancy! This discrepancy is much smaller however. Under standard cosmology it's a factor of 10-100 times, under MOND, the mass discrepancy is usually in the neighborhood of 2. In other words, under MOND, there's still matter in the universe that we can't detect by its light, but the missing mass is small enough that it can be explained by normal matter that's to dim to detect. This is why things like the bullet cluster are actually expected under MOND. I don't know the particulars of this exact galaxy, but it's possible that the radial velocities that astronomers measured for its stars have a high enough margin of error such that it still fits within MOND's predictions. Something I've noticed is that MOND is still fringe enough that you can't necessarily trust non-MOND physicists when they talk about it. One thing is for sure however, this galaxy is as puzzling for Dark Matter as it is for MOND.