The answer is simple. He plays taller than almost everyone else in the NBA. The NBA added two new fields to their predraft combine measurements this year. A no step vertical reach and a max vertical reach. What's somewhat interesting is these fields have always been measured, just never listed.
Vertical is actually measured by calculated by taking the vertical reach and subtracted the standing reach. They aren't trying to guess how many inches a guy is off the ground.
Back to the topic at hand. No step vertical reach is probably the best indicator of how tall someone can play. It shows how much height someone can get without a running start. Of the players who've had vertical and reach tested in the combine only Greg Oden among legitimate players in the past nine years has a higher reach than Tyrus (though several others are tied).
This underscores what a dynamic athlete Tyrus Thomas really is. When it comes to running max reach only Shaq and Rudy Gay have higher max reaches than Tyrus in the history of the database, and Shaq's number was based on an old newspaper article not an official report, so is considerably more dodgey.
Just something to consider before deciding whether to throw Tyrus off the island.