Interesting question. It could be that it was illegal for a local to own gold or that much gold. It could be that the gold came from a robbery, whether carried out by a local or one of the invaders killing a fellow soldier for the loot. It could be that a local who, for example, supplied/sold food he grew to the invaders would have been set upon by his fellow countrymen as a traitor. I have no idea which among those theories (or others) is favored by the folks who deal with these finds. Those coins are spectacular, IMO.
Simply fell out en route or left behind after falling out at camp.
It really isn’t likely anything that exciting.