Unclear, in that credible sources and reports have been suggesting very different findings. Our understanding of human immune response is partial, and there are plenty of remaining questions. So I'm not shocked or surprised, but do regard it as good news that they have found that outcome.Unclear in what way? That the data wasn't in, because we do have a very good understanding of how the human immune system retains genetic memory of previous infections in order to fight repeat infections. So unless SARS-CoV-2 was from some completely new, previously unseen genetic line there was always going to be the possibility that infection would have the same effect as other viruses. And as early as a year ago evidence was emerging that people who had no exposure to it still had some level of pre-existing immunity, suggesting that exposure to other viruses of similar genetic sequences could be the reason for this.
This latest research shouldn't be too much of a shock, well with perhaps the exception of the people seemingly wanting the virus to be worse than it actually is, or at least for the restrictions to go on much longer.
Meanwhile, I repeat my observation that this is good news if the results in that paper are representative and sustained. As with all good science, I'd expect researchers to be trying to reproduce those results and validate the outcomes of what's been published - and if they can't, to publish those findings too.