During the period of the Scottish-English union, the state was collocated with the island, so it's an appropriate term. The point Bill is making though is that "Great Britain" was a valid geographical term at least back to Ptolemy, so if someone wants to say someone was born in Great Britain, there's no Wikitree historical context where that isn't a valid and meaningful designation, and it suffers no ambiguity during the period 1707-1800.