I am not 100% sure about sweedish law, however I would assume that customers are not liable for unauthorized transactions on their account. If a transaction was charged twice then they would not be liable for the 2nd charge (if they only authorized the first). Also this is almost certainly a UI issue as the bank would likely have not actually sent the money to the merchant accounts, and even if they did the funds are generally not available right away so it could easily be reversed.

I know that the above is the case in the US.

This is also not a "double spend" in the same way that bitcoin prevents "double spends"