Anomaly is about right, could be outlier too... I think your suggestion of Czech origin could be more likely than Murano, thank you for the pointers. I have a sneaking suspicion that it is from another source again. Just had a look at Tamara Aladin and Riihimaki, purely because of the concentric rings on the base, nothing obvious to find though.
From what I can remember of the opalescent Selena from Orrefors is that the entire body is opalescent, thick walled and uniform. This flower vase has a thin opalescent layer cased in a much thicker layer of clear.