Wouldn't the lack of standing be an aspect of the merits of the suit? In any case, the supreme court isn't the sole judge of the merits of a case, they are just the arbiters of the outcome.
So while the suit was thrown out for being obviously faulty, it did not fail "on its merits." Mind you, that does not make the objection sensible. If I write "they are bad because they are a poopy face" in crayon, and then I don't pay my filing fees and the case is thrown out for that reason, I am technically correct that my case was not heard on its merits, but that doesn't make it a good point.
The Supreme Court can reject a case for lack of standing (the plaintiff does not have the right to sue the defendant) or for lack of merit (the lawsuit is obviously frivolous). They can also reject it if they think the lower court ruled correctly, but that doesn't apply here.
Your confusion is 100% reasonable because there is _conceptual_ overlap between standing and "who wins." For example, one aspect of standing is "injury-in-fact." That means "you suffered a harm recognized by the legal system." If the court says no standing because no injury-in-fact, to a layperson that's similar to saying "stop crying, go home." Which sounds a lot like saying "you lose the case."