Well, that would certainly explain it, but the researchers say this:
"The virus appears to mutate very slowly, with only tiny differences between the different strains and that none of the strains of the virus are more deadly than another, experts say.They also added it does not appear the strains will grow more lethal as they evolve."
Do I believe that? I don't know. I don't think anyone really knows anything definitively yet.
As for the other assertions in the paper, they seem to contradict what "Next Strain" found. I linked to it above. Take a look and see what you think. More eyes and brains are always better than one. :)
They do seem to show two different entries into Europe, one from China directly, mediated mostly through Belgium, it seems, and one perhaps from Singapore. I can't tell from the map if that was directly from Singapore, or if it was mediated through Australia. However, although Italy does show up there as one of the infected countries, there don't seem to be any subsequent samples with that particular mutation from Italy. So, how could most of the cases in Italy be of that strain if their sampling was representative?
There are other strains into Italy from the "parent" one from Belgium.
I could be all wrong about this, let's be clear.
For what it's worth the original paper by this group was criticized in a lot of quarters.
https://nextstrain.org/narratives/nc.../zh/2020-04-10
As for Sweden, they seem remarkably comfortable, to me, with saying well, they're old, they were in poor health anyway, so that's a blow we can absorb. That's even before it was known there were lasting effects in people with severe cases.
I can only say I'm glad my elderly relatives don't live in Sweden.