I'm sorry to hear about your ticket. In terms of appeal, if the judge's decision was premised on a credibility issue it is harder to appeal than if the judge mistook the law. If the judge believed the traffic officer's version of events--i.e. that you were not in the car and not unloading a passenger--then it is harder to win on appeal. If the judge believed your version of events and still found you to be in violation, then it is a misinterpretation of the law, which is easier to prevail on.
The fact that you were in or out of your car is not the issue, however. The rules of NYC include definitions for the words used in violations:
Since the signage only prohibited "standing," I will only address that particular definition:
Standing. The term "standing" shall mean the stopping of a vehicle, whether occupied or not, otherwise than temporarily for the purpose of and while actually engaged in receiving or discharging passengers.
As you can see, whether your car was occupied or not is not relevant to the definition. What is relevant, however, is that you were there temporarily to offload a passenger, which is an exception to the prohibition on standing. So based on your version of events, you would not have been violating a prohibition on standing. If the sign had prohibited stopping, for example, you would not have a leg to stand on because that would prohibit the stopping of your vehicle for any purpose. But a mere prohibition on standing should not have applied to what you were doing.