It is related to the legnth of the mech. but I don't think the limits as stated ^^^ are a true reflection of the capability.
The shorter cage needs a shorter chain and will not allow shifting to the larger cassette sprockets when on largest chain ring;
Obviously unless you are a novice, you would never choose that gear combination but select smaller chain ring and smaller rear sprocket.
You would be able to use say a 29T or more cassette with the granny ring on the front.