word for false nostalgia

Nostalgia is still the correct word, because it being related to some personal association to a historic place (even if it is false). For example, with pirates, you might see a guy with an eye-patch and a parrot and think "Oh! A pirate.". However, if someone who had never seen movies or read books with pirates with those characteristics, then they would associate it with pirates.

Another example could be thinking about home. If you grew up in a coastal city, you might think that the smell of fish smells like home. In reality, most homes or cities don't smell like fish. You would still be feeling nostalgic if you related the smell of fish to your hometown.

I hope this helps.

"Idealization" can also be used for this concept. We tend to "idealize" something from our past or our history that may be just a fantasy version of that person, place, thing or time.