In Japan gays can't marry but adult adoption is legal. So technically they are going to be father and son, but it's only on paper. That way they can be a family without the legal bind of marriage.
In addition to Laughing Wolf's correct assessment, the one yelling was sounding an awful lot like a father yelling at his useless son. LOL It was a perfect combination of moments for that response.
i don't get it.. in the last one why, 'Dad'?