This hilarious play is known as a comedy of manners precisely because it does what your quote expresses. Any comedy of manners takes as its basis the social customs and behaviour of its day and then uses that as the basis of satire. This is particularly true in the way in which such texts depict relationships between men and women. This is why this text concerns social pretenses so greatly. In this play, we are presented with a world in which society forces women to deceive and act coyly in the merry dance of courtship and couples deceive each other in their marriage and even friends deceive each other. Marriage is shown to be more about wealth and convenience than actual love.
Congreve presents us with a world therefore where moral values and principles are exchanged for prestige and wealth. In addition, the deceit that is practised by all characters makes this play incredibly comic. In this play, the words that characters speak and the way that they act to each other are almost never a reflection of what they really believe. Consider Fainall as an example, who, if we look at appearances alone, we would imagine to be incredibly happy in his marriage. Reality however shows us that he scorns his wife and is having an adulterous relationship with the best friend of his wife.
This conflict between appearance and reality exposes the way in which Congreve is satirising his own society and how this society was based on the importance of maintaining an outer facade or veneer of wit and sophistication, no matter how questionable the reality was underneath that veneer. Congreve indeed uses this play to hold a mirror up to his own society and to find it wanting.