Yemeni authorities, with assistance from the US military, seized a dhow in Yemen's territorial waters. The boat was loaded with weapons, explosives, and cash. Yemeni authorities believe the boat's cargo originated in Iran, and the US agrees with that intelligence assessment. If that suspicion is confirmed, it would further complicate US-Iran relations.
The trouble is the Yemeni government has long used Iran as a boogey man, sometimes rightly, but often times to win political points. As to the goal Iran might have, most likely they are trying to "needle the Saudis" in every way possible.