"The Springfield Soccer Association tells the station that a misprint in the team’s roster identified Hernandez as a boy".  If the team roster "mistakenly" listed a player as being the wrong sex in a same sex league that would be the first time in history that was done, because no roster in a same sex league even includes that as a category.  To top it off THEY'RE EIGHT.  There's no real physical ability difference at that age.  If anything, girls tend to be a little bit more mature and further developed in motor skills at that age.
Far more likely, there's an overzealous parent or parents that want an excuse as to why their kid lost and want to blame it on the kid that looks different.