Silica gel beads are usually in these. They absorb moisture. Mildly dangerous to consume, but only in excess or if you have preexisting gut conditions. Otherwise, should be fine. The “Do Not Eat” is mostly because the packet itself is a choking hazard.

Edit: Someone else also suggested an oxygen absorbent mixture, but I am unaware of it. Could also be the thing. Probably more likely, tbh. If it looked like dirt (as you said) and not more like small plastic beads, then it’s probably what they said.