sojiro just thinks it'd be weird to hear akira call him dad, and then in the very next line says "actually, maybe that wouldn't be so bad". it implies that he realizes that he wants to keep their family together, and that akira and futaba would actually be really good for each other, but people only read the first half of the line and use it to justify something that makes literally no sense ¯\_(ツ)_/¯