Pluto's planet status

Traditionally, "planet" meant "wanderer". And pluto still wanders around the solar system. With the traditional meaning, it is still a planet.As you indicate, the real change was to the definition of "planet", which has now been made more precise. And science does periodically refine its terminology and improve its definitions.A lot of scientific change is really change in definitions of terms and concepts. So the change of the status of pluto is really a pretty good example of scientific change.

This gets into the subtle question of whether TRUE and FALSE are applied the syntax (the string of words), or to semantics (what that string of words mean).As applied to syntax, what you were taught is now false. As applied to semantics, what you were taught is still true, but the same string of words no longer means what it did at that time.

Once upon a time, everything did orbit the earth. But then some busybody name Copernicus stuck his nose in, and things have been messy ever since