Yes, it's his sister.
I have come to believe that anything is possible with family history.
Have just checked the Jersey census. He was 8 in 1871, so he'd be 17.
He's supposed to be a year younger than his sister.
One never knows about ages. His mother lied about her age when going to New Zealand from Jersey. She made herself younger, of course. I bet Mr Belet didn't know that!