When Jones landed the takedown, it was because Gane was radically out of position on the feet. Gane threw a super-aggressive looping step forward power punch and stepped past center, actually turning his back to Jones and leaving his hands completely out of position to defend the back takedown.
The thing is, it wasn't something Jones had seen on tape and prepped for; he actually needed some time to react to Gane's mistake. That also means it isn't something Gane was expecting or had prepped to defend. Gane hit panic mode, and while it didn't finish him immediately, he also didn't stop panicking until Jones stopped him.
Gane definitely shit his pants.