Hi this is my first car so not an expert on these things yet, but my other half took my car to work and now this has happened to the tyre, it looks like someone has put a knife or something into the tyre, but maybe I'm wrong, what does everyone else think?
Tires I have seen which are intentionally slashed have knife like slits or have a shape from a sharp spike. This doesn't look like any of them, however when that happened, your tire went flat quickly. So it likely happened close to where you parked. Any recall of anything you might have run over? It doesn't look like you hit a curb or something like that, because there is no scuff mark.
Near the top of the picture there is debris similar in color to near the penetration.
Good luck figuring out the source.