https://en.wikipedia.org/wiki/Grumman_LLV

The "ton" truck rating persists, but it's mostly outdated. The F-150 is a "half-ton" truck, despite having a rated payload capacity that's often closer to 1 ton. I drive a "1 ton" truck that can haul over 2 tons ...

Those are load ratings. 1/2 ton is still a standard small pickup parlance, but a a true load rating that probably hasn't been true since the 70s or 80s. Back before then it was a good idea of what you could haul (as opposed to a "full sized" 1-ton)