Little is rarely black and white. You are assuming that the item was imported to the UK for sale; maybe it just arrived in the UK in somebody's household goods. It may have been sold through the US base shops in the UK. Maybe the manufacturer just marked everything the same regardless of where it was going.
If it had been destined for the US market, then legally it would have had to state country of origin. I'm not sure about the legality of marking a product as 'foreign' and selling it in the home market would be allowed. These things tend to be determined by treaties. If for example it were made in Sweden for sale in Finland, would English be used?
Just to throw another thought out there....just glancing through Andy McConnell's 20th century glass there is a brief mention on page 15 of anonymous 'Foreign' stickers / labels 'as commonly applied to Swedish 1960s glass'
This is news to me and I appreciate anything that adds to my (often limited and sometimes stubborn) knowledge. I look through Wayne's 20thCenturyglass.com's 'Hooped' glass section shows some cousins if not brothers and sisters.
We know as a general rule that German ceramics (would it follow that glass was similarly marked?) were no longer marked 'foreign' in the '60s. As I understand they switched to 'Germany' as quickly as they could because it was popular knowledge that German = Quality. Is it possible that Scandinavian glass companies were trying to cash in on the confusion as 'foreign' marked goods disappeared from the shelves in the hope that people would think their goods were German? Unlikely, when Scandinavian glass was being emulated around the world. I find the quote "'Foreign' stickers / labels '
as commonly applied to Swedish 1960s glass" a little surprising - although I do not dispute it as I have no evidence.