It's not unadulterated good news. As too often happens when the Greens are invited into a ruling coalition, they will govern alongside two centrist to center-right parties: in this instance, the two most major of the nation's major parties, Fianna Fáil and Fine Gael.
The main angle of the article is that, on Saturday, the Daíl Éireann (Irish parliament) officially elected Fianna Fáil leader Micheál Martin to be the new Taoiseach (prime minister), succeeding Fine Gael's Leo Varadkar. But from another angle, in particular from the left, this is not only burying the lede but straight-up omitting it.
The article does not mention that, following February's Daíl (parliamentary) elections, the Green delegation jumped from three seats to twelve of the 160 total. GP will be the fourth-largest in the 33rd Daíl. Other parliaments in Europe have recently experienced a Green surge.
Apart from that, it also misses the point of why the two major parties must coalesce in the first place: Sinn Fein's leap from 22 seats to 37. Sinn Fein, a center-left party that was once the political arm of the Irish Republican Army, has more seats that Finn Gael and nearly as many as Fianna Fáil. Unlike some other parliamentary democracies in Europe, where disenchantment with mainstream parties has led to right-populist victories, the Irish electorate has veered left.
This Guardian article from two weeks ago hints that SF might end up at the head of a governing coalition for the first time in the Republic's 100-year history; the GP's acceptance of Fáil & Gael's invitation to join them thwarted that.
Also worth noting while we're here is that Ireland elects its parliament from multi-member districts of three to five seats each, with proportional representation, via a single-transferrable preferential voting system. This assures that "minor" parties are represented in the nation's law-making body. And it's not some recent innovation: It dates back to the first general election following independence from Great Britain in 1922.