That long pipe fell from the sky at the same time the core stage fell from the sky, so it's a good bet that's from the LM-5 core stage. Just because the core stage's debris "fell into the sea" doesn't mean every last piece of it did.Are you saying it was something else besides a piece from the core stage? Like what? What are you claiming this long pipe is if not a piece of the core stage, or where it came from if not from the core stage? You'd have to start going to Trump's Conspiracy Theory Central if you want to say this is some kind of intentional Western plot to make China look bad. No, this long pipe is from the LM-5 core stage that fell onto earth last year. Every other explanation for this pipe's appearance in the Ivory Coast last year at the same time that the core stage de-orbited requires some degree of intellectual dishonesty and/or conspiracism.
This is also mostly besides the point. If since 1990 other spacefaring nations have taken extra steps in their rocket designs to not let their debris from their larger stages fall onto land, even if the risk of harm is small, why doesn't China do the same???