You were correct in questioning this order. I wouldn't worry about the incident report, you acted in a manner that any prudent nurse should.
For that instance that is way too much ativan 10mg sounds more like a Valium dose. If he was an alcoholic and were worried about DT's that could be an acceptable dose depending what his CIWA score was.
Exactly why I would have questioned the dose, I would have wondered if she hadn't confused the dose for ativan with valium. We follow a CIWA protocol at my facility, the physician can order a Symptom Triggered Therapy or a Fixed Dose Therapy of either valium or ativan. Approximately 1/2 of alcoholics will have a cross addiction to drugs, so higher/titrated doses may be necessary.
In the OP's situation, the ativan wasn't being prescribed for alcoholism and his history indicated anxiety. Normal dosing for anxiety would be 1-2mg or 2-6mg po in divided doses, not to exceed 10mg in 24hrs.