It doesn't matter if the incoming cable is capable of 100A, it still doesn't mean that supply has a capacity of 100A.
DNOs apply diversity just as electricians do, the capacity of the distribution transformer determines how many supplies may be connected at 60A, upping some customers to 100A may well mean a larger transformer is required.
One cannot assume that because a certain size cable, fuse carrier, meter etc has been fitted that there is capacity.
I doubt the fuse has been changed, the meter fitter is likely to have removed the fuse, fitted meter, refited the fuse, applied new seals, and applied a label showing the fuse size.