It is likely that the reason the lid slots are not straight is to prevent wheelchairs from getting stuck in them. Maybe that’s why the lid is marked as "disabled friendly" by the wheelchair icon on it.
The lid is similar to another manhole cover made by the same manufacturer
GS - Spheroidal graphite cast iron - a special cast iron in which the crystallization of carbon has been slowed down, which makes it close to steel - also called ductile iron (Thanks to Vuori Susi for the clarification)