The user unconsciously influences the movement to what they hope or what they know, there's not any science behind it. I've only had one male feather in slow and I've had chickens for over 20 years, so feathering in rates aren't a set in stone way to guess gender.
Yes, unfortunately that's a Cornish x. On a restricted diet, they can usually make it to a year or two.
On a different note, I know many find it cute, but you don't want to encourage them to ride your shoulders or head. It's a bad habit and is dangerous for you and them.
X2 your friend needs to call the game service and come clean about, they may not fine her.
If the game service or police find them, she will be fined and the birds will likely be culled