I've been lucky enough to see one Iridium flare in my life. Def not what I'm describing. But it was cool as hell.

My honest opinion was an astronomical event, like a nova flash

I've seen this phenomena with Jupiter and the moon before, but it doesn't describe what I've seen.

Imagine you're looking at an empty point of sky on a clear night. Then a blip of light appears, just for an instant. Now it's gone.

It didn't move across the sky, didn't shine or flash. It just appeared and disappeared.