A lot of the "Mystery names" on the list sounds an awful lot like made-up Swedish towns (I'm assuming that if they were real the author would have found them). E.g.:
Bergsbo - could be a made-up town name, but it could also roughly be translated to "mountain dweller".
Bertby - Would literally translate to Bert (Swedish boy's name) village.
Biby - Bee village.
Billsta - -sta is a common suffix for places in Sweden.
Bjurön - Bjur is an old name for beaver, and the name literally translates to Beaver Island. Furthermore, bjur is (according to the Swedish National Encyclopedia) a common prefix used in village names. https://www.ne.se/uppslagsverk/encyklopedi/l%C3%A5ng/bjur.
The official "keeper of place names" in Sweden is Lantmäteriet, the Swedish geodetic survey. Unfortunately, the search feature at minkarta.lantmateriet.se seems to be down at the moment. However, OpenStreetMap lists at least five islands or islets named "Bjurön", several neighbourhoods, villages and such named Billsta, two farms named Biby, a village named Bertby in (largely Sweish-speaking) Österbotten in Finland, several villages and farms named Bergsbo, etc. My guess would be that nearly all of those names that are plausible Swedish place names actually exist somewhere.
Bergsbo - could be a made-up town name, but it could also roughly be translated to "mountain dweller".
Bertby - Would literally translate to Bert (Swedish boy's name) village.
Biby - Bee village.
Billsta - -sta is a common suffix for places in Sweden.
Bjurön - Bjur is an old name for beaver, and the name literally translates to Beaver Island. Furthermore, bjur is (according to the Swedish National Encyclopedia) a common prefix used in village names. https://www.ne.se/uppslagsverk/encyklopedi/l%C3%A5ng/bjur.