It’s fairly simple. When we say “duplicate topic,” it doesn’t always mean “exact copy.” It’s an overarching term that we use to describe topics that have similar intentions. The goal is to avoid clutter and unecessary topics, so if there is a topic where your thoughts can exist, then your thoughts should go there. Similar topics are allowed only when they merit seperate discussion.
For example, when you created your “Thank you” topic. It’s nice that you were thanking people, but we already had a topic where that could go. Because your topic shared intentions with the Thanksgiving topic, it was moved over there. Your topic didn’t merit enough discussion individually to be kept separate, and so was closed.
Obviously that’s not always the case. We have a general Star Wars topic, and yet a Solo topic. Could the Solo topic be moved to Star Wars? Sure. The former obviously falls under the latter. Will it be moved? No. Why? Because Solo merits enough discussion to have its own topic. Another big exception is Creative Content. It’d obviously be crazy to have all MOCs or all artwork in one topic, so those get individual topics.
In sum, just look around before you create a topic. If you see a topic that would cover your thoughts, even if its old, put your thoughts there.