Not 100% sure but they could be Springtails(
growdiaries.com/grow-questions/39905-white-strange-insects ). The other is like ojeterpelon said mealey bug. If you can see how they react when in a jar of water. If they spring(shoot) really fast across the water around 1" at a time they most likely are. In which case they are harmless to the plant, but usually stress out the grower 😃. As for the look, Your correct in you just flushed them and now they are hungry. When I need to do a flush once I complete the flush I finish it with a light dose of the usual feed to make sure they have something.
Good luck and Happy Growing