This only seems newsworthy because of the recent fatal crashes. Trains separate all the time. Admittedly, most of them aren't travelling at high speeds while full of passengers, but still.
Still not a good look for the closest thing that Murrica has to HST.
"All the time" is a bit of an exaggeration, but fatigue in knuckles should be caught normally, and good train handling should prevent it, though shit does sometimes just happen.
I'm 99% certain that the Acela sets are semi-permanently coupled, which would make this event more noteworthy.