Board Thread:Naruto Discussions/@comment-34436445-20180703141210/@comment-1512913-20180705124641

Maybe Sasuke explained it off-screen? Naruto/Sakura/Whoever: 'Sasuke, about your Rinnegan... it looks somewhat different' Sasuke: 'What do you mean?' Whoever: 'It has six tomoe in it... it kind of look like the Sharingan, ya know?' Sasuke: 'That's because that is Sharingan dumbass'

Pretty much.