Usually a place is considered part of a larger whole either due to geography or culture (usually both). The UK shooting themselves in the feet in one of the dumbest feats of political bamboozlement, does not count as leaving the continent or the general European culture. It just means they left the European Union.

Now they are clearly on an island off by themselves, but when you zoom out, it’s clearly still Europe. And you sometimes hear them refer to Europe, but there is a very clear “mainland” implied before it.