They are probably referencing their vote in the 2014 Scottish independence referendum, in which they presumably voted yes, but which ultimately failed.
I don't have any skin in that particular game, but if I were Scottish I would be absolutely livid with how they were treated. Just one example:
Scotland is by and large in favour of the EU. During indyref they were told that leaving the UK means leaving the EU, they chose to stay in the UK, then England dragged them out of the EU a mere two years later anyway.
Sewage has long been a problem in UK rivers and on UK beaches.
The current regulations are not enforced, so introducing stricter standards would have precious little impact unless the regulators grow some balls and teeth. Right now, sewage companies are allowed to dump raw, untreated waste water (yeah, poop) into the environment under certain extreme circumstances, however, in their interpretation, those circumstances include it being a Wednesday..