Actually, just looking at it a few times, the first punch landed by the Georgian seems to rock Johanneson to his boots. His left leg looks unsteady even before he tries to throw one back and slips on the advertising on the canvas.
I think he was genuinely hurt.
I think Carl has the makings of a good fighter, he's not really spectacular in any area, but he has a great work ethic, and is solid technically, plus he really seems to really enjoy the fracas.
It's the first left hand that did the damage, you can see Carl's legs buckling slightly, and he looks well discombobulated when he tries to fire back just before getting hit.