It seems unclear what happened here.
You can of course be "protected" on a later flight without being booted off the first. If you are rebooked, however, it doesn't matter if you had a paper boarding pass or a mobile one. The paper boarding pass wouldn't have allowed you to board either. So "that's why I print out my boarding passes" wouldn't necessarily have helped here. The GA would have scanned it and said "I'm sorry this isn't valid".
I'm not sure which happened here, but could be either the app to blame or not app related at all.

Either way, I agree it seems histrionics to say it "ruined your trip" when a flight delay on a close connection results in taking a IAH-DEN flight less than 2 hours later. I doubt there was some sort of important meeting tomorrow that made the difference between arriving in DEN at 930pm v. 1125pm on a sunday such a major travesty. Nor would either arrival have much quality time with young kids.

If a 2-hour delay "ruins" your trip, you planned poorly.