I *think* I know who this is.... Anyways, I'm glad you pointed out it is a gate agent, not a flight attendant as the author of the piece titled it. (He corrected himself in the comments field, but did not change the title)... Although this behavior is not acceptable, we cannot have 100% of our staff perfect. I hope this letter gets to his superior and the two can discuss it one on one and possible ways of handling the situation differently.
There is no absolute way of confirming this event but I do believe this occurred.