Pollard was not convicted of treason.
Passing on national secrets is treason, no matter what the plea bargain.
He wasn't tried for treason. He pled guilty of lesser stuff and accepted a plea bargin. The judge threw out the plea bargain, as was his right. Now, for those of you who think that it is rare, it is not. It actually happend to me once. I was arrested on some felonies (over-reaching, it was some fraternity prank stuff) I accepted a plea bargin for a fine. The judge threw it out and sentenced me to 500 hours of community service.
That does not mean that I was not guilty of the felony charges (even though I think the felony aspect was over-reaching).
Similarly, Pollard elected to put himself before the judge, the fact that by accepting a plea bargain he was not tried is not good proof that he was innocent.