I think we can also judge whats going on with other peoples children by their cries. I can make out an "I want that!" cry compared to a "heartwrenching" cry. It sounds like the OP noticed it was not just a tantrum, but that something was going on.
I experienced this at Wal Mart once. A lady had two toddlers and a very obvious newborn. The newborn cried hysterically while she walked through the store for about ten minutes. My mama instinct wanted to scoop him from his infant seat and soothe him desperately. I kept thinking she would pick him up at any moment, but she did not. She stood in line for ten more minutes while this teeny, tiny baby sobbed. She paid, and headed out the door while her newborn screamed. Even stopped to get the toddlers gumballs. There was NO excuse for that and it took all I had not to chew her a new a-hole. Seriously. She was obviously not in a hurry at all, but could not tend to a newborns needs. Ugh.
Yes. I have 4 kids, from 20 all the way down to 2. I know there was something wrong--I know those cries. It just kept escalating and the poor child was so tired from the experience. It appeared to everyone around (because they all said so!) that he had just completely given up that his parents were there for him. Like that tiny baby who is left to CIO alone and learns not to trust that his parents will be there.
And I've heard the newborn thing, too. I can't stand it. It makes me hurt in my heart. One time my dh and I were Christmas shopping at Target. This woman was there w/her baby in a bucket/carseat and it was a TINY baby. My dh had our youngest in a sling, and he kept pacing in front of this lady, pointing to his sling and making cradling/pick up your baby motions w/his arms. She.just.kept.looking.at.a.stupid.watch while her baby cried pitifully all by herself.