Hi. So when Pin Trading was started for the Millennium Celebration, no one thought that it would blow up to what it did. WDW found this profitable new revenue stream, and so the other divisions were eager to cash in. But since they didn't PLAN for doing Pin Trading outside of "1 year at WDW", there was a window before they could beef up other division's pins into greater production. Disneyland solved this by re-releasing a bunch of designs from pins produced in 1998 but with year 2000 backstamps, the Cruise Line solved this by stocking and selling several WDW styles with DCL backstamps.
It's not a fake. It's just indicative of a pin that was purchased *on a ship*, instead of WDW, during this window after Pin Trading became popular but before there was a plethora of DCL specific pins. Think of it as how some pins sold at US parks are also sold at the International parks, but those have different backstamps than the US pins.