Impossible to tell without more information.
What were the blinds ? What was his table image ? What kind of player is the guy with AKo ?
My guess it how it went down: Everyone folds around to the button, button raises it with his AKo. SB is tired of button raising preflop every time, and he has a pair, so he pushes over the top. Button actually has a hand for once and calls. It's a coinflip, and SB wins.
If that's how it went down, and they were both shortstacked (15-20BB maybe), it would be a correct play from both of them.