A member of the British upper crust can correct me if I'm off the mark, but the definition there is of a really existing usage, and then the example doesn't match it at all. Did you make the example up yourself, by any chance?
There is, in ordinary people's language, "yeah, it was quite good", when talking about a movie or something, which could easily mean, it was moderately ok, not amazing in any way. It'll depend entirely on tone, you could say it in a chirpy tone and you'd mean that it was actually pretty good. This is the most common usage, and familiar to our brothers and sisters and non-binary-siblings across the pond, I suppose.
And then there's your mathematics teacher saying, "Oh, this lemma really is quite trivial", meaning it's very, very trivial, or a "quite difficult proof", meaning you've to drag yourself across hot coals for hours before it hits you.
Then there is also the meaning you describe above! E.g., a bunch of aristocrats are having dinner, and the candelabra suddenly breaks loose, flies through the air, and smashes into a thousand pieces with a crash. Luckily, no one is hurt.
Everyone looks around, shocked, there's a few shrieks of course, and then one of them says: "Oh, what a smashing evening!" and the other says, in a bored drawl, "Quite". It's like an additional layer of being removed from and above the mere idea that the original thing could have been worthy of a positive comment (in this case, the dinner).
There is, in ordinary people's language, "yeah, it was quite good", when talking about a movie or something, which could easily mean, it was moderately ok, not amazing in any way. It'll depend entirely on tone, you could say it in a chirpy tone and you'd mean that it was actually pretty good. This is the most common usage, and familiar to our brothers and sisters and non-binary-siblings across the pond, I suppose.
And then there's your mathematics teacher saying, "Oh, this lemma really is quite trivial", meaning it's very, very trivial, or a "quite difficult proof", meaning you've to drag yourself across hot coals for hours before it hits you.
Then there is also the meaning you describe above! E.g., a bunch of aristocrats are having dinner, and the candelabra suddenly breaks loose, flies through the air, and smashes into a thousand pieces with a crash. Luckily, no one is hurt.
Everyone looks around, shocked, there's a few shrieks of course, and then one of them says: "Oh, what a smashing evening!" and the other says, in a bored drawl, "Quite". It's like an additional layer of being removed from and above the mere idea that the original thing could have been worthy of a positive comment (in this case, the dinner).