Indeed, there's a size limit on reportable winnings that trigger the necessity of a W-2G. There's also potentially different requirements that trigger tax withholding by the payer.

It's generally $600 for winnings, and $5000 for withholding.

https://www.irs.gov/pub/irs-news/at-01-17.pdf

https://www.irs.gov/pub/irs-tege/gaming_withholding_reportin...