Take a look here. The issue isn’t buying the lotto ticket. The issue is sending the winnings overseas.

edit: more detail

Foreign asset control at the federal level is the regulation. You don’t have a fundamental right to send things or money out of the country. Only as allowed by law.

Interstate commerce will differ from international commerce. The first has significantly lower barriers (freedom to do business between states, and travel between them). The second is tightly regulated.

There is almost certainly federal law regulating this kind of situation. You can’t just send an amount that large overseas without declaration. It may be entirely unlawful to do so if the recipient, or their location, is subject to foreign asset control status.

Also, somebody likely owes some taxes, and it doesn’t matter whether he/she is stateside. Tax jurisdiction attached to the money the moment it was won.