The aerial shot (Birdseye View) on Bing.com/maps, shows that you are correct. The shot looking east shows that not only were the houses built on fill, there was cut right about where the failure occurred. The cut appears to have been to allow the construction equipment access to both the top and bottom of the slope. Quite likely they didn't properly fill and compact it. (Some of the shots from other directions show the houses already built, some of them anyway, but the one I'm thinking of shows the site prep in progress, but no houses right there.
Do you think we can expect the party or parties at fault to have sufficient liability coverage for this?