Ha, I notice you don’t say how you liked the dish with fish mint. I’ve only had it as part of Vietnamese herb accompaniments, and found the overly fishy taste quite off-putitng.
I take it from your description of the dark object as “bark” that it wasn’t edible, and may be a chip of wood that might be used to smoke pork belly. Or could it be a very dry, extra fried piece of smoked pork with skin (I could see that seasoning the oil, which could season the whole dish). The fresh pork looks nicely cooked.
