the speedo can be calibrated.
when you do that, the odometer becomes correct.
most folks that lift trucks are kinda clueless, so a lot of them are just left inaccurate.
My guess is that the dealer has something stating that he bought it that way, and the that odometer reading is inaccurate. as part of the contract.
the actual miles on that truck will be the least of your worries...
(I have zero Florida experience)