When you help a chick, the gunk can sometimes glue their feathers down. I don't know how they do it, but when they hatch naturally, they can clean that stuff up so they dry fluffy. You can rinse them off in warm (100 degree) water and give them a good warm place to dry off if you wish but all that stuff does not come off just rinsing. Some people probably use shampoo, dishwashing liquid, or something else.
I had that happen once, the chick that became shrink-wrapped. It was still alive in the shell after I took the others out so I helped it and left it in the incubator to dry off. It had a lot of down glued down so I rinsed it. Helped some but not a whole lot. I’d given the other chicks to a broody hen so I picked off the shell and membrane but left that down, then gave it to the broody after it was very dry. She accepted it with no problems and in about a week that gunk was gone. I could not tell which chick that was. She raised all 15 chicks.
I had that happen once, the chick that became shrink-wrapped. It was still alive in the shell after I took the others out so I helped it and left it in the incubator to dry off. It had a lot of down glued down so I rinsed it. Helped some but not a whole lot. I’d given the other chicks to a broody hen so I picked off the shell and membrane but left that down, then gave it to the broody after it was very dry. She accepted it with no problems and in about a week that gunk was gone. I could not tell which chick that was. She raised all 15 chicks.