Unusual Play in NCAA game

[rulesmaven]

Washington v. Illinois in the 2d round of the NCAA tournament.

Second made free throw by Illinois player. Ball is put at the disposal of the Washington player behind the endline under the basket in which Illinois has just scored. Official starts counting five seconds. Washington player places the ball on the floor, out of bounds behind the end line, and runs into bounds. Another Washington player comes from in bounds to out of bounds, picks up the ball, and looks to pass it in bounds. Official (who had momentarily suspended his count due to some apparent confusion) continues the count and the Washington player calls time out before inbounding just before a five count.

I've never seen this play before. I could not find it in the rules. Is there a specific rule allowing the player to place the ball on the floor out of bounds? May any player from either team then pick the ball up without liability for being OOB?