Verrrry interesting !
The curves are identical. That means that at every instant of time, the ball's horizontal and vertical displacement are equal.
That means that however high off the floor it is, it's exactly the same distance from the wall !
The ball is moving along a 45° diagonal path. It's like one of those contraptions with a ball connected to a wooden paddle by a rubber band. Any direction you hit the ball with the paddle, it goes out in that direction, and then it comes right back to the paddle.
-- This ball begins at (0,0) ... where the wall meets the floor.
-- For the first 3 seconds, it goes straight out at a 45° angle. However far from the wall it is, it's exactly the same distance up from the floor.
-- After 3 seconds, it's 4 meters from the wall and 4 meters above the floor. It's at the point (3, 4) on both graphs.
-- Then it stops going out, and comes back.
-- After 6 seconds, it's back at the point (0, 0) again, where the wall meets the floor.
