Did the manufacturer start to call Chevrolet vehicles by Chevy or did word first evolve from general public?

While Chevrolet has used "Chevy" in its marketing, the nickname wasn't a deliberate launch from the manufacturer. The shortened form "Chevy" evolved organically from the general public. It's a common shortening of a brand name, similar to how "Coke" is used for Coca-Cola. Chevrolet eventually embraced the nickname as part of their branding, but it wasn't their original creation.