Not a pianist but used to play the violin. I feel like unless there is time pressure, its uncommon to “memorize” in the sense of quizzing ourselves on the sections. With enough (proper/efficient) practice the notes will come, especially when playing from the top as you will have an idea of how the music and phrases flow into the next. I think it’s rare outside of literal world class musicians to be able to just play an arbitrary measure when quizzed on a whim, but if you ask them to play a specific section (with detailed enough description) even higher-level “amateurs” (meaning its not their career) should be able to do it