Why is this news? In fact, why is the fact someone tweeted for the first time even on HN? It's utterly inconsequential and about as intellectually gratifying as memes on /r/adviceanimals.
Do you get how news works? Lots of people are interested that the Pope, not just some dude, is tweeting. Therefore, it's news.
Cool, another high profile person has joined the 'looks like a famous person on twitter but is actually a large PR team' club.