I think the difference is that yes, Sandra did win twice against non-winners, as you say. But more important is she won the second time against non-winners AFTER having already won the first time. The second group of non-winners knew going in that she was a previous winner. If they had been on top of their game, they'd have voted her out to prevent her winning a second time. Tony doesn't get the same kudos, because the stakes were different this season. Him winning this time was against only previous winners, so somebody this season was going to be a previous winner who won a second time - against previous winners. He can claim to be a "winner among winners." Not the same as what Sandra did.
She will always be queen, and Tony will always be, er... Number two. LOL!
Dave