The first touch is always about receiving the ball and passing it cleanly to the setter. The second touch is about setting up the attacker (if possible). The third touch is a spike or other attempt to get the ball to the other side. The only significant decision points are usually who the setter chooses for the attack (among 2-4 players depending on formation), and on the defense side, where the blockers jump (3 players choosing spots to cover). Since the algorithm only predicts "actions", both of those don't matter (the setter is going to be "setting" regardless of who they choose, the blockers are always going to be "blocking" regardless of the spot they cover).
The "team strategy" part is in effect just a check of whether the algorithm knows what is happening on the court at all. Volleyball allows the aforementioned three touches, and what the team is doing for each touch is pretty much immutable (the only source of variation is if one of the "steps" fails).
This is of course still an achievement, but the choice of sport gives the researchers a leg up, since volleyball has significantly fewer "degrees of freedom" than other sports. In that context, ~80% accuracy at predicting an action 2 seconds out is less interesting, and it's unlikely that it's anywhere close to human performance for this particular sport.