On the Portal leaderboard, there are four players with a higher score than is currently possible. They have 276, but the highest score is 262 (what everyone else has). If you look at the four player's profiles, you can also see that they have not unlocked any of the achievements and they have no "date finished" on the leaderboards.
It seems the scanner got confused when checking those four players and gave them wrong scores.
Portal Achievements