If you look at the design it looks like Roman Empire. Not a single Nusantara, Siamese or Arabic design element on it.

Actually the answer to why we never hard metal or leather armour is because these materials never reached this part of the world before trade started. If there was metal done in trades, it was most likely used to make purposeful products like nails that could build house and boats. And used to make knives and probably machete for working on food and processing jungle produce. It is stupid to think armour was the first use when metal is a valuable commodity for food, shelter and probably weapons. I do not think metal spear heads ever made publicly available to the people besides the royalty that used it for guards because they could afford them.