Basically how it must have happened (my headcannon is Luke would have named his own son Ben, but probably thought he'd never be able to have his own...he thought his sister's son was going to be his legacy)
You know what? This is very important. Not very many 18 year old boys would do this and because he does it shows how big of a heart luke has. He cares so much for his fans and is accepting and amazing. Luke hemmings I love you!