[ESL students: 'journalism', like 'traffic' and 'mail', aren't words that are themselves broken into quantities, and so aren't pluralized. '5 traffics' is nonsense, like 'a traffic', and will make people frown. Secondly, 'doing journalism', while better, is still lazy for verbs like 'literally' is lazy for adverbs]
it's a manner of speech used jokingly. similar to how someone "does an oopsie" where, you might find, "an oopsie" isn't a specific activity that someone performs.