The ball from Stones comes to Otamendi's left foot, if he was left footed, the ball back to Ederson is very simple. The fact he's naturally right footed forces him to take a touch back on to his right foot, as he's clearly not confident playing that ball back to Ederson under pressure left footed.
It's exactly why I have advocated signing Ake as a Laporte backup before Koulibaly, as that situation even if unpunished happens a dozen times a game. Someone posted a video a while back showing multiple occurances of our problems playing out to that left hand side when Laporte is missing, I wish I had saved a copy. Can't be arsed finding it but whoever posted it might remember and be able to re-post it.