On Graham Greene's "entertainments"

Anyone who's read older editions of Graham Greene novels knows, from the list of his works int he front pages, that he distinguishes among his fiction publications between "novels" and "entertainments." I'd never read any of the so-called "entertainments," but yesterday started Our Man in Havana and find it, yes, entertaining. But what's the distinction, exactly? Aren't novels entertaining? Especially "comic" novels such as, say, Confederacy of Dunces? It seems, though, that based on this novel GG was not interested in or aiming for believable characters or plot - he's interested in comic, uproarious, even preposterous situations, all of which must be close enough to reality - and also close enough to the kind of romps we've all seen in various screwball comedies that we don't dismiss them out of hand. The premise alone of Man in Havana is illustrative: a British businessman (sells vacuum cleaners in a little shop w/ one employee) in Havana gets recruited, much against his will (initially) by a spy from British intelligence to serve as eyes and ears in Havana, 1958, with a rebellion fomenting against the (unnamed) dictator. HQ back in London makes the assumption (wrong) that the vacuum guy (Wormold!) is a big businessman, and he quickly realizes that they will pick up a ton of expenses (e.g., country-club membership, ostensibly so that he can make contacts but in fact so that his spoiled daughter can ride her horse) in return for detailed reports, which of course he fakes. In one, he sends sketches of what he suggests are implements of mass destruction in the Cuban forests; in fact, they are sketches of one of his vacuum cleaners. So yes, this is a lark and meant to be - it's not The End of the Affair or The Quiet American. I do wonder whether GG always knew exactly which what his works in progress would develop: Could have have started Man in Havana as a serious novel and then got captivated by the comic possibilities? Or could he have thought of the Quiet American as, at first, a potential comedy but then the characters and setting led him on another pathway? I think it's informative that GG recognized the distinction between his two fictional genres, but in a way I think he's selling himself short on the "entertainments." Interestingly, both the entertainments and the novels have been adapted into fine films.