Looking it up, it was there for a maritime exercise, but the navy had also participated in the parades in India (this is where I got confused); it was a diplomatic affair and the ship (not a sub) didn’t even have ammo, as required by the event (or at least both India and Iran say they didn’t have ammo, the US government says otherwise).

They had some minimal ammo for a few events, low in amount and only enough for specific drills and not enough for any battle and certainly much less (if any left at all) after the drills were done

https://apnews.com/article/iran-israel-us-iris-dena-warship-submarine-8789cf718b1ebf8b571cb8ef5d785150