Underwater platform most likely.They’re on schedule, first 4 will be delivered by 2023-24, second 4 will be delivered by 2028. We might also see one Type 039B (not a hangor) be delivered before those for training purposes, as the naval chief did hint on that too.
I also doubt that, such a major defense deal would likely not stay hidden. I think the launch was from a 90B or a non-submarine underwater platform.
Unless Pakistan made its own submarine (unlikely), such weapon deals being hidden is a rare thing.