I wouldn't trust the same AI overview that once told me that the Atlantic was the world's largest ocean.
He should watch the last night of the Proms.
There are several different versions of God Save the King, so "knowing all of it" is a vague target. Typically only the first verse is sung on official occasions, so hearing it in its entirety is rare. Even the official Royal Family website doesn't have all of it.
So what? Patriotism in the UK is different to how it is in the US, it's a lot more private for one thing.
For example. The Flag
I had a house in Florida, one of perhaps 12 houses on a lakeside development and built from new with a flagpole. all the owners had the US flag on display.
There was a recent movement to display the English flag outside your house
Note that it is different from the Union Flag
There was a lot of fuss, including the main TV news, that this display of patriotism was being hijacked for political ends and the enthusiasm for displaying the English Flag softened considerably.