The stopper on mine is equally unusually large (almost out of proportion), so it will be useful to confirm there are at least two bottles with oversized tops!
I suspect I had initially hoped Blenko, but the quality is not there, I don't think. The blue casing is of varying thicknesses all over the beast, the colour is not remotely "consistent" and there are lots of small bubbles in it too, in some, the white casing shows through (on the bottom part of the stopper), there are "wonky" bits on the rim, it's not a neat, tidy finish.