[Zuph]

The cruising altitude of Google Loon's is well above the cruising altitude of any commercial jet. This accident was caused by a balloon coming down, a much rarer occurrence.

I don't expect to hear a postmortem from Google, but I'd be astonished if this wasn't a malfunction of some sort-- These balloons almost certainly have an emergency cut-down device of some sort capable of safely and rapidly returning the payload to Earth.