Some myths are based on fact. How fast a chicken feathers out is based on genetics. If you breed a slow feathering female top a fast feathering male you can tell the sex of the chick at hatch by looking at th ewing feathers. Not a few days after hatch but at hatch. That is the fact.
The myth is that you can tell the sex of any chick based on wing feathers. Many people on this forum believe that myth but it does not work that say unless you know how the parents are set up genetically.
Do you know how the parents of that chick were set up genetically? If not, you will be just as accurate flipping a coin as looking at the wing feathers.