Bull****. If the ecm was left in the bike and dash updated, it would have re-paired with the ecm when installed back on the bike and power applied.
If the dash was updated, it will come back as blank or zero miles, so the only way they'd have gotten around that is to replace the ecm as well. Wouldn't matter if it's a stock or race ecm, as long as it was "brand new" out of a box, that's the ONLY way the dash could possibly show zero miles. I had that option on the last RX I rebuilt. Turned out it only had 16xx miles on it, way less than was thought. Had to completely replace the dash and repair the wire harness to bring that one back from the dead, along with a lot of other stuff.
Dealer in question does not know enough about that bike to be considered reliable for information.