I'm seriously amazed at how polished it looks after just a small rinse of water over it, despite being buried for over 3000 years. The arrowheads also look perfectly intact

Ah, so the real answer is that the sword was bronzed

"Given the soft nature of bronze, historians have previously wondered whether such blades served a ceremonial purpose, rather than a practical purpose on the battlefield. A few years ago, scientists even staged sword fights in order to learn more about how the Bronze Age weapons could have been used effectively in battle, despite being much easier to damage and harder to repair than their iron successors."

Scientists a sword fight?! Yes:

https://www.smithsonianmag.com/smart-news/en-garde-scientists-stage-sword-fights-study-bronze-age-warfare-180974705/