There are actually two different questions. Generally, the Many Worlds interpretation says that when an observation is made, reality splits so that there is now one new branch for each possible observation. Is that what happened in the reported experiment? No. You have two observers, both occupying one reality but reporting two different observations, as evidence by the fact that they are able to write a paper together to report their different conclusions, and that one paper is presented in one reality. This says nothing about whether any realities split, only that in one reality, two seemingly contradictory observations are reported.

The second question, “How would we know if reality splits?” seems to be unanswerable. And if we can’t know it, then it is mere speculation, not science. (Similar objections have been raised to cosmological multiverse ideas. How can we know, or more precisely, how can we test for it? If we can’t, then it’s not science.)

I think this result is very interesting, but probably because it raises the question, “Do we need a different interpretation of quantum mechanics than any so far put forward?” I don’t know the answer to that, but it may be worth asking.