Can you add a photo for us?

Try feeding them crickets again and see if its forms up. In general though, their poop should remain normal. Could be a coincidence. It's never a bad idea to have his stool tested though. Especially if the poop stays runny. Give him a day on crickets and see what happens. If the stool does stay runny, collect a clean sample and have it tested soon. Infections are easier to treat the sooner they are caught. I think I would send one anyway to be safe. Lay down some paper towels near his feeding area to hopefully collect a clean sample.

Keep us posted.