I was in a situation like this one once, only I was the administrator in question, and I was the one coming under attack from specific members of the forum community for banning said individual when he started abusing his power behind the backs of the other moderators and administrators of said forum.
There are men and women behind the scenes. Nobody besides them knows what's going on back there. To presume you know is to be incorrect.
They do not have to give you a reason why a particular person is banned. For the same reason, you may not understand why a particular person is banned. In this case, you were provided with a valid reason--that this particular individual was engaging in deceptive practices generally--and evidence that doesn't involve pulling back the curtain--that this particular individual was using pictures that weren't his own to represent himself.
When I was the administrator at another forum, I banned a relatively well known individual for hacking the forum. But it wasn't just for hacking the forum. His reason for hacking the forum was to try to obtain evidence from a moderators-only forum that the site owner wanted to ban particular popular people that he didn't like on the forum (which wasn't true). He actually found a backdoor into the moderator forums and had been visiting it regularly for some time with the tacit knowledge of an administrator and another moderator (it was a large group in control of that forum).
The general population didn't know he hacked the forum or what his motives were for doing so and I wasn't about to report to them the particulars of what he did. They also didn't know what the other administrator and moderator who were "on his side" were doing. That banning, however, led to a thread much longer than this one of people questioning my actions, questioning what's going on "behind the scenes", and so forth. In the end, we simply said that he had hacked the forum, which was ban-worthy, and the admin and mod that had been in the know with him were asked to leave the team and the site on their own (which they did--they were in on it b/c they didn't like the site owner anyway).
Anyway, long convoluted story, but my point is that there is more behind the curtain than you might think. And sometimes not everything needs to be revealed to the general population on the forum because it would serve no beneficial purpose. And sometimes an excuse can be found for banning a troublesome person that might not be the full reason, but rather the simplest one to explain.