Adding comments into C++ code before functions and properties marked as UFUNCTION and UPROPERTY respectively makes them show up as tooltips in the editor when hovered over.

You can prevent this by prefixing it with a ~ symbol:

//Shows up in editor
//~Doesn't show up in editor
UFUNCTION(BlueprintCallable)
void MyFunction();

(source: https://x.com/KristofMorva/status/1816405720411066608)