It was probably just a general interest piece to help sell newspapers. If the coins were found just north of Donner Lake, from what I understand from maps on the "Donner Party" they never even camped at that location?
The coins were probably loot from a robbery somewhere possibly from Yerba Buena, or possibly even Sutters Fort.
Probably not a bad place to hide them, a lake would be a pretty good landmark, to pick your loot up after the heats died down.
Indians must of got him. Either that or he was caught red handed and hung.