"It could be many things, but ...
Strong preservation magic must have been used on the structure, but since the corpses have degraded so much, they must not have been affected by the preservation magic. It makes no sense that they wouldn't stop the rotting which means the people who made the structure likely didn't kill these people. That means that they are likely not native to this shard.

So yes it could be a necromancers cache or other things, but I then I do think he was a local.

Also if we follow that stream's direction then it should lead to a water source that the people who lived here used.

But that might be dried up..."