He said he liked the show, but he was only being 'polite'. [=he did not like the show, but he said that he did in order to show good manners]
He is not, 'to put it politely' [=to say this in a way that shows good manners], the best guitar player in the world.
When she called the painting “unique” that was just a 'polite' [='nice'] way of saying she didn't like it.
(..) - Hey, that's mine! - Rusty, that's yours. Come on, Rusty. Good morning, everybody. Welcome back. Before we begin, just a polite reminder. Could we please have silence during the games? Right. Please wait for the buzzer. What's he doing, the Sicilian? Yep. (..)2014 The Dark Horse