I can totally understand, the American example would be.

As a kid you are told about Santa Clause and his little helper elfs.

Now that you are an adult you have learned that the elves are actually bases on slaves and the color of their skin is als based on that.

To you it’s just an elf and you never associated them with history or slavery. If fact as a kid you are told they have this color from the chimney.

So in reality both are true, people that grew up with zwarte Piet are not necessarily racist, but the entire tradition is based on historical context and therefore racist.