Basically he’s saying use Pluto’s year to define which year in light year you use to calculate a light year. Normally you would use Earth’s year. Since Pluto’s orbital period is ~248 years your “light year” has gotten noticeably longer. If you express a distance in what would have been a few light years in real light years, in this new scale it appears as a percentage and looks like a small number. The distance hasn’t changed though.