Technically true, which as we all know is the best kind of true. Note, however:
“The United Kingdom (along with the British Overseas Territory of Gibraltar) was a member state of the European Union (EU) and of its predecessor the European Communities (EC) – principally the European Economic Community (EEC) – from 1 January 1973 until 31 January 2020.”
https://en.wikipedia.org/wiki/United_Kingdom_membership_of_t...
Compare the start of this subthread: “Didn't ARM start in Europe?”
Whatever point it is that subsequent responders were trying to score by mentioning continental europe is moot: Britain was part of Europe in more ways than merely its location.