The nova acted as a rendezvous signal, causing all starlines connected to that star to flare up. Otherwise it's too hard to find aliens - opening starlines is expensive. It's the chance of a direct encounter (small) versus chance of at least one mutual neighbor (larger).

Even so, for reasons of which you are very well aware, meeting two sets of aliens should be a _lot_ less likely than meeting one set, so we ought to take that in account when we are trying to make sense of what is going on. But I accept that positing a minor god is rather a primitive reaction, especially as we already know that in your impossible possible world no Singularity is reachable by any means currently envisaged.