Unless I'm mistaken the UK hasn't drifted off and become and independent island chain separate from Europe
Sometimes people make mistakes, sometimes outright errors. Sometimes people use language to push ideas they like, such as "the EU is Europe" and thus not being a part of the EU is somehow an offence against nature. I'm not sure why these mistakes, errors, and mendacities should go unchallenged and uncorrected.
Every use of "Europe" in that article could be replaced with "EU" and it would be the better for it.
The problem is the there’s no specific term for the people living in either the US or the EU, so we “wrongly” use Americans and European.
Note: I say this as both a US|EU citizen.
Some would argue that's exactly what happened but your point is valid, EU != 'Europe the continent'. The problem is that such imprecise usage is rampant.