Read further down in the article. What the ECJ ruled was once invoked, article 50 could be revoked by the state who invoked rule 50. Nevermind the political consequences of this and that this was after Brexit was in the works. So the ECJ’s and by extensions, the EU’s rules on this are being made up as they go, in ways which can be turned around to support the EU.
The ECJ was considering the question only because it had been asked to do so by a Scottish court, to which it had originally been put by the anti-Brexit devolved Scottish government. Whether or not the effect of the judgement will be to strengthen the EU in any particular case, the fact remains that it puts into a member state’s hands a power which the EU had thought it owned. The EU Commission, in its submission to the Court, held that Article 50 could only be withdrawn if all 26 member states agreed. The ECJ rejected this.