Absolutely, positively, flat out impossible.
The MT1000 (like most single-band radios) can be stretched a few MHz +/- out of their normal bandsplit, but no single radio could even so much as cover the entire band it operates in, to say nothing of the utter impossibility of it operating across multiple bands as far apart as VHF and 800 are.
Not to be a dick, but you were totally BS'd by the seller if he told you he had VHF, UHF and 800 programming within a single radio, and it somehow worked properly. "Hacked RSS" or not, it's BS, plain and simple. And as far as you personally verifying that the radio "transmitted and received well" on all three bands...well let's just say that I think it was either wishful thinking on your part, or you're not quite sure what you're looking at, or you have a really good imagination!