What a tragic story!

As Bob said, strange things can happen with trailers. I was driving on a freeway near home in Ohio many years ago. The median was a wide grassy area. All of a sudden a trailer with a maybe 23-foot powerboat detachd from a vehicle that was coming the opposite direction. The trailer proceeded off the road and into the median and coasted until it came safely to a stop. All I could think about was, "What might have happened to an oncoming car if this had happened on a two-lane or four-lane highway with no median strip."

We have had two different trailers totally depart from the tow vehicle. In both cases it was because the tongue broke aft of where the safety chains attach.

In one case it was because an additional section had been welded to the tongue to either raise or lower the coupler (can't remember which), and the weld broke.

In the other case the trailer had a long, unsupported tongue, and it broke right where it meets the triangulated sections that go out to form the main bed of the trailer.