You don't have to understand fundamentals like aerodynamics and lift or be aware that heavier-than-air flight is possible to notice that paper folded in a certain way can fly quickly and predictably. Which came first?
Here are some past responses to your question:
Did people make paper airplanes before the airplane was invented? with responses from u/AshkenazeeYankee and u/svendskov
Did people fold paper into paper airplanes before the invention of the airplane?, responded to by u/svedskov
Did paper airplanes exist before the Wright Brothers?, responded to by u/cthulhushrugged
You might try these threads:
Did people make paper airplanes before the airplane was invented? with an answer by u/AshkenazeeYankee
Did paper airplanes exist before the Wright Brothers? with an answer by u/cthulhushrugged
Can I ask a follow up question? Why did people treat manned flight as a practical impossibility before (and even after) the Wright brothers first flight?