Sora wasn't confused about it. Riku wasn't nobility, and he had grown up differently. That was all. Sora wasn't going to stop him from enjoying the things he had before.
"I will not be good at it, I am sure." It was a children's activity, which is why he suggested it to Abe, who should not be forced to do adult things ALL the time. "I have not done it since I was a child." And he wasn't going further into the water than his knees. Maybe. He made it to the shore and wiped his feet on the grass.