I agree, JC. I've had a guy who rode behind me tell me my Bushtec would hop once when I would hit some of the worst junctions between the interstate and a bridge. But it would only hop once, then it would settle right back down. I can't remember even feeling it hop, but that's the way their supposed to behave if you hit bad transition seams like that. It sounds like that guy hit something with one of his trailer wheels and it flipped it, although with a regular trailer ball, I'm left guessing how that could happen. I suppose a Bushtec could do a complete flip, since the end of the tongue will turn freely 360 degrees. Naw, this guy hit something really big. That's the only way it would flip.
IMHO, if you're gonna ride a bike much less pull a trailer, you gotta develop a routine and nail your setup each time you start on a trip. If you approach it maturely and take your time, you should never have to worry. The other side of that - and maybe even more importantly - is that you have to drive smarter than when you're not pulling a trailer. Allow more room in front of you for braking, expect traffic lights to change, practice emergency braking (especially two-up), and in general, be sober about it. And of course, remember there are two more wheels behind you and give debris in the road plenty of clearance!