I was going to say that maybe Yuuta and Rikka went directly to Touka's apartment, but I realized that it's hinted that Yuuta dined with his family (which is why his sister asks where he is after she is already cleaning the dishes) and Rikka dined alone.
I didn't quite think about it during the first time I watched the episode but Yuuta most likely imagined Rikka eating alone while watching at the leftovers. This is probably when he started to realize how lonely she is, and that's probably why he decided to start cleaning.
In other words it's not like Yuuta has the same OCD of the MC of Toradora, that was his way to show his sympathy to Rikka.
This is one of the reasons I really like this anime, there's so many little things that you can only see when you pay close attention to them.