The original data seems to be available at [^1] but I dont see any spike around the 22-23 of June ... Let's wait to know more before saying anything stupid (looking at you Greenpeace)
That system you linked only measures radiation.
While the sensor in Sweden actually sample the air to detect certain isotopes.
STUK does have this type of sensors also and did see these same type of isotopes in the air[1].
[1] Announcement in Finnish https://www.stuk.fi/-/helsingin-ilmassa-pienia-maaria-keinot...