There were no dramatic changes in IPs for Unisource's account, which would suggest there was no account theft. There was a round played on a Punkbuster-enabled server, which had no third-party anti-cheat setup on it. My assumption is that since PBBANs declares it as a "Cached Data" ban, then the ban was originally 'created' on that server. Punkbuster does not always ban you immediately if it catches you in the act, attempting to 'keep the cheater guessing' for when they got caught.
Now, I'm not outright saying that Uni was cheating, but I am also not ruling out the possibility. There are many different things that could trip PB. For example, I believe that "Sound Radar" programs that come with Soundcard Bloatware is something that would trip the cheat detection. If Uni uses Cheat Engine (a memory editor) for other games, that would quickly set off PB if left running in the background, as two examples.
Unfortunately, we don't know specifically what the ban was for, since it didn't get logged to PBBANs.