My initial thoughts are for that to occur, there can only be a couple of events that have changed.
The RPM of the speedo drive. However, that cannot have happened with just an inner cable change, so you can discount that possibility!
More likely is the proximity of the rotating magnet within the speedo itself. If that has been pushed closer to the needle centre (the part that receives the magnetic 'signal' from the rotating magnet) that will increase the amount of 'drag' & the consequence will be higher, faster readings.
I hope that helps as from memory, when I used to bother to try & 'calibrate' speedos, it was a tweak that would work, to an extent