That figure was the market cap, the price at which a token was sold multiplied by the number of tokens on the market.

If a billion tokens are available, the market cap is $0.5B if you sell a single token for $0.5. That's what happened yesterday more or less. You won't be able sell all tokens for $0.5B, so saying they are worth $0.5B is misleading for such a volatile and young project.

The metric works much better (but not perfect) for established shares, financial products or contracts for physical objects.

It was named after a vegetable and vegetables meme well in Ethereum because a subset of Etherians like to "yield farm" and identify as yield farmers.

I hear their self destruct feature works pretty well

They took the best features from a number of different projects and gave an equal opportunity for all participants staking to earn tokens. Most other tokens/projects have been VC funded with an uneven number shares allocated to early funders (aka pre-mining).