No story spoilers please, I'm only on MB 6.

But yeah, I've been wondering about that cause at first I thought it was the fully little ewoks but then I noticed they look lie they got kind of a hunter gatherer technology level.
They walk around with metal containers to pick up and gather stuff, definitely not required if you have the technology to build something like the towers / tunnels.

And who built the mechas?
Are they invading Lilipa or their own security systems gone haywire (sorta PSO ep 1 mine style)?