Why did Sett win when they didn't control both battlefields?

Ruling: You can win by holding a battlefield (controlling it at the start of your turn) to gain your final victory point, even if you don't control both battlefields. The restriction requiring control of both battlefields only applies when conquering (scoring during your opponent's turn), not when holding.

Sequence:

• Sett deck held the battlefield with Pit Rookie
• Volibear deck removed only the Sett unit
• Sett deck started their turn still controlling the battlefield with Pit Rookie
• Sett deck gained a point for holding, which was their final victory point

Nuances:

• When conquering, you need to have scored the other battlefield this turn (though you don't need to control both simultaneously)
• When holding, there is no restriction about controlling both battlefields