Questions about CNY70 Reflective Optical Sensor datasheet
Figure 1. The graph is scaled in an unusual manner.

If I was doing this graph I probably would have used 0 as "edge on centre of target" and then used +/-5 mm for the adjustment. These guys are saying that 0 is covered with 5 mm beyond centreline.

As we might expect we get 50% current when the target edge is on the centreline as half the maximum light will be reflected.

The various curves are a function of the beam angle. The closer the target, the narrower the beam and so full or zero light is reflected with a smaller deviation in 's' from the centreline.