They do indicate the region, and it does include sweden, finland, large parts of baltics and certain areas in russia: https://mobile.twitter.com/SinaZerbo/status/1276559857731153...

Had you included the full quote you would have known why they did not point out the exact location: "We are able to indicate the likely region of the source, but it’s outside the CTBTO’s mandate to identify the exact origin"

If I interpret it correctly it means that they do not know the exact location and other organisations will now have to investigate it further to get the exact origin.