If you think there is wiggle room in that definition, you would be mistaken. Article 6 is explicit about where attacks will trigger responses. Vessels in the Mediterranean Sea are mentioned explicitly.

Article 6 (1)
For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:

on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France (2), on the territory of or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;

on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.

(1) The definition of the territories to which Article 5 applies was revised by Article 2 of the Protocol to the North Atlantic Treaty on the accession of Greece and Turkey signed on 22 October 1951.

(2) On January 16, 1963, the North Atlantic Council noted that insofar as the former Algerian Departments of France were concerned, the relevant clauses of this Treaty had become inapplicable as from July 3, 1962.

More
http://www.dailykos.com/story/2010/5/31/871525/-Israels-attack-tests-NATO-Doctrine.