From the other thread where this was discussed:

  In the "Emergent Magnetic Charge" section, second paragraph:
  "Finally, we emphasize that the observation of emergent monopoles is fully consistent with the modelling of AFM topological textures in Fig. 2 and does not violate Maxwell’s equation as they are, in fact, sinks and sources of the H^ field."

  So this is a collective effect of a bunch of magnetic dipoles, and they go on to describe how div B is indeed zero in the material.

https://news.ycombinator.com/item?id=38549099

So this is not a Maxwell's Equations violation or anything, it's just some 'trick' to make a field that somehow locally looks divergent.