Basically he did two things wrong:

First and less important, he hasn't trained well with UFC rules. He still uses the ring to train, and by the looks of it hasn't bothered to worry about defending elbows from his back

Second and most important: He overlooked Gonzaga. He didn't look like he was taking him seriously....he barely threw any strikes outside that one kick that Gonzaga caught. He spent most of his time parrying and circling without really doing anything back. Even during the kick, I almost think in his head he honestly didn't believe that Gonzaga would be able to launch a kick to his head....you can clearly see him going to block a body shot.

Hopefully this lights a fire under his ass so he can get back into gear.