I'm thinking this doesn't happen?
It did happen to me, as per video. OR Engineer came in, looked where I wanted ONT, installed ONT, working inside & outside property. Once he was happy with his tests, he asked for me to test with my equipment (router & laptop running speedtest), whilst he put tools back in van, did some 'paper work' in van, came back 10 minutes later and checked I was happy with connection.
It does make sense that customers test the service before OR leaves, rather than customer call later and have to have a repeat visit.