An interesting article.
If I was a betting man I would my money on dark matter.
The trouble with MOND is that scientists have had a history of tinkering with gravity if things don't agree with theory.
A MOND like theory was introduced in the early 20th century to explain the perihelion advance of Mercury's orbit when astronomers were unable to find the hypothetical planet Vulcan which could explain the anomalies in Mercury's orbit.
GR explained the phenomenon and the MOND theory was relegated to the dust bin.
The thing that has bugged me about cosmology is that maths indicates a matter component to the early expansion of the Universe in an era where the Universe was dominated by radiation. The effects of "ordinary" matter only came into being later during the post recombination era approximately 100,000 years after the BB.
The presence of dark matter in the Universes very early history fits the bill nicely.
Steven