It’s against their own terms and conditions to not KYC you for such a large win, in line with their gaming license.
9.2. Sportsbet.io reserve the right to carry out additional KYC verification procedures for any withdrawals exceeding the equivalent of 1 Bitcoin or €2000 as regulated by our gaming license. Account Holders who wish to recover funds held in a closed, locked or excluded account are advised to contact our Customer Support.
Normally I would side with the cynicism of the gamblers in the proverbial battle, but if you examine the clause closely you need to respect the careful semantics: they
reserve the right to carry out verification. They don't need to, but they have the ability to: that is what you're agreeing to.