Well, in the view of the law in the U.S. an inherently hazardous activity is something which carries very significant risks if not done correctly, significantly more severe than some concept of ordinary activities. Using dynamite in an excavation project is an example I seem to recall. It's very hazardous stuff, if it's not done the right way. The mode of transport has become very safe and reliable . . . but when the proverbial Swiss cheese holes fall or are pushed into alignment, "smoking hole in the ground". Thin aluminum tube, 30 thousand feet, perhaps Mach .8, not easy to walk away from something gone wrong.
Claiming injury from traumatic sightings of the engine in failure mode would not already discount for the safe return of the flight to Denver. I'm not a hundred percent convinced this is an actual claim being filed, but if it is, the suit would assert the injury being claimed didn't get canceled out by the fact of the safe return.
Of course there are the lawyers of ill-repute, chasing ambulances. There also are very highly experienced and effective attorneys who vindicate the rights of people harmed or killed by the kinds of negligence, malfeasance and other wrong-doing so knowledgeably decried on this and similar forums.
And I'd have to see it to believe it - how any advocate could present this case in a court of competent jurisdiction and give proper respect to the pilots, yet still claim the (supposedly) injured passengers are entitled to anything.