The only incongruity is agnostic (not knowing about gods' existence) posting "their god wants" (claiming to know what god wants) -- ridiculous.
. . . not irony :
Why not irony. Seems to fit these given usages.
incongruity between the actual result of a sequence of events and the normal or expected result
(2) : an event or result marked by such incongruity
b : incongruity between a situation developed in a drama and the accompanying words or actions that is understood by the audience but not by the characters in the play