Good grief....it was a table in a coffee shop. I have never seen a table reserved for handicapped only restrooms stalls and parking spaces but never a table. The man was apparently able bodied enough to make the extra effort to walk up to your table and instead of kindly calling the mistake to your attention he chose to bang on it with his cane. You made a mistake but handicapped or not, he was being a jerk. What if he was sitting at that table and someone more disabled than he, such as a quadriplegic in a wheel chair, came into the shop? Would he have gotten up and walked on his two legs over to another table? I'm guessing not.
We need to be considerate of others and to comply with the ADA laws but people are going to make mistakes and blunders. I'm always puzzled by people who get all moralistic about things like this. It seems to me most of them aren't all that concerned about disabled people, it's more about them getting to feel extra virtuous for a few moments or appearing noble to others by making sure everyone knows they are on the "good" "or popular side of an issue.
Anyway, this whole topic reminds me of that Seinfeld episode where George parked in a Handicapped parking space in the Mall.