Riku's journey as a volleyball player was pretty strange. Even though he started practicing from a young age, he had never joined any formal team before.
His school life before entering Tsunemori was non-existent, considering his father put him in a luxurious private school where most of the students came from an important family and had huge sticks on their asses – which explains why there was no volleyball club since those people thought that a sport that left them sweaty and smelly was beneath them. As for joining a non-school team just like him with the Thunder right now, that thought crossed his mind once, before his mother realized his grade fell off and decided to pull him out of the club.
So, yeah, even though Riku was no stranger to volleyball, he was basically still a rookie in the game.