Malaysia is a common stop on the way from China to mask country of origin - which China does a lot especially to avoid sanctions and tariffs. Many items that make into the US still originate in China but are trans-shipped to other countries and relabeled.

It is now being reported that the ship was carrying duel use items such as chemical precursors for rocket fuel. IRGC was also onboard. Iran was testing the blockage and they needed the supplies. If that ship would have gotten through it would have been a huge propaganda win against the US.