I agree that there being something rather than nothing is evidence that God exists but is not evidence for what kind of God he is. God is the source of being, so he does not add to the “things” in existence which require explanation, but is rather in himself the explanation for everything else which is dependent upon him for existence. If you look outside and see lots of trees blown over you might remark that the wind caused the trees to fall over. If someone said that answer was no good because “it doesn’t explain anything, because where did the wind came from?” we would think the objection doesn’t really fit the conversation. One gets the sense that skeptics who ask for an “explanation” for God, as if he is the next on the list after the universe to be explained, are not listening to what believers understand by “God”. Because God is understood by many believers to be the uncaused ground of all being, not an item or thing in the universe to be explained like any other.
Saying that God is the reason for existence may not exhaust everything there is to be said or that pertains to existence, or to God himself. But it doesn’t mean the utterance is without meaning or content in itself either.