Earlier quoted context omitted.
He looked over the Na'vi bio-networking quite superficially. But his point was that how can a rhinoceros destroy a robot like that. It's like you take an armored elephant against an M1A2 Abrams.
We're talking about technology and life forms that don't exist, but imho: The rhinoceros was huge. A couple bullets, even from the robots, will not stop something that size in it's tracks. The robots are smaller, flimsier, and seemed to posses lesser firepower than tanks. Elephants have armor and defense nowhere in their body. The rhinoceros in Avatar looked like they had a veritable carapace to me.
The rhinoceros was about 2 times the mass of the robots (even they seem light, in realty they shouldn't, different composition, eg. man and a humanoid). The gun was at least a .50 cal. With all this advancement in technology, AI should guide the gun to Aim at the knees (technology that exists today, evaluation of damage trough pre-imposted data).
And yes, you're right, it's just a movie.