Can bearded dragons evolve genetically over 2 or 3 generations?

I was at a party where the host had bearded dragons. She explained that one of the lizards didn't like the tank being so large. I asked why that would be the case since, when they were in their natural habitat, they had vast expanses of desert to traverse. Her friend, who is a doctor in genetics, explained to me in a very condescending tone that it 'obviously' evolved genetically in an environment of small tanks and therefore I had no reason to come up with my own doubts as to its agoraphobia...