you are right. i thought the seaside resort ostia was a separate city/town, but it is in fact the 10th district of rome (municipio X). thanks for pointing this out!
The International Hydrographic Organization's publication Limits of Seas and Oceans specifies that the eastern limit of the Mediterranean is at the Dardanelles, which excludes the Sea of Marmara from the Mediterranean and therefore also Istanbul from this list. That jives with my other research which cannot find anything that suggests the Sea of Marmara is a part of the Mediterranean (including Jetpunk's own Seas of Europe quiz!)
Adding "city" to Gaza, Mexico, Kuwait, Guatemala or New York is nonsense in a test that is specifically asking for cities. It's not part of the name, it's just used to disambiguate in places where there may be confusion.
Good quiz, but I do not think there is any logical reason to include some marginal seas (Aegean, Adriatic) and exclude others (Marmara, Black, Azov). I understand that the latter are geographically more separate from the "mainstream" Mediterranean, but nevertheless are part of it, not least historically and culturally. Crimea was no less a part of Ancient Greek world (and of the merchant networks of the Middle ages and early modern epoch) than Crete or Sicily.
If you are interested in cities and the Mediteranean Sea, check if you know the /www.jetpunk.com/user-quizzes/190926/biggest-mediterranean-island-cities>Biggest Mediterranean Island CIties!
I believe Paris is in the northern part of France, so it would be in the North Sea area, rather than the Mediterranean, and that's even if it borders a sea.
According to Wikipedia the entire Gaza Strip is just over 2 million people and Gaza City is right at 600k. I know we are taking numbers from citypopulation.de but that is a heck of a big difference. Only thing I can guess is they consider the entire territory to be a single metropolitan area.
It is indeed the same with Kuwait and New York, but not with Mexico City and Guatemala City, both of which have 'City' as part of their official name.