What is the figure of speech in line four of "The Unknown Citizen" by W. H. Auden?

The fourth line of W. H. Auden's "The Unknown Citizen" is the following:

That, in the modern sense of an old-fashioned word, he was a saint.

In the context of the poem, this line could be viewed as an example of satire. The unknown citizen is described in terms of his conformity to social expectations: he was a satisfactory employee at a factory, had moderate and acceptable reactions and opinions, headed a nuclear family with the correct number children, and owned a number of consumer goods. The social satire in the poem arises from the claim that regardless of whether the man was "free" or "happy," the important aspect of his life was that he lived correctly according to the normative standards of being a good worker and consumer. The use of the word "saint," specified as the modern usage of the word, and claim that the unknown citizen serves the "Greater Community" provide a sarcastic tone to the poem, because these claims are in no way supported by the details provided about him. There is no mention of the unknown citizen serving others, so this suggests that in modern society, conformity is viewed as saintly.