I'm just guessing here but it could be that in this particular situation Hero covers Button (stack size pretty much double). So he can "afford" to call wider, and try to eliminate the smallest stack from the table since there are no other players in that hand.
because on BU you have two players left and in this situation BB has too great odds to fold most of his range. You just fold total trash, but rest of the hands is +ev, because math doesn't lie.
The button is also so short and giving you such great odd to see the 5 cards to come. You almost getting 2 to 1 odds here. When you thing of how wide he is pushing here its easy to have a big range yourself as you end the action.