That is clearly absurd, therefore your definition of disembarkation must be incorrect.
You make a valid point. Yet, as you point out, the definition of disembark as used in the Aeronautic Act is ambiguous. Clearly "disembark" and "evacuate" have different meanings, otherwise we would use the same word to describe each event.
Neither term is defined in the Aeronautics Act.
And since the Aeronautics Act specifies that a flight ends when the doors open for the purpose of "disembarkation" and not "evacuation," we cannot automatically assume that evacuation and disembarkation are equivalent for the purpose of this section of the act.
This is why we have judges. We delegate to them the responsibility of resolving ambiguities such as these. But a judge can only do so if a case comes before him/her in court. That is why we need to start charging people under the Aeronautics Act when they try to retrieve their bags during an evacuation.