As for me;well, we know that he possessed some wisdom in explaining 'The Great Circle of Life" to Littlefoot.
Yes, at his age, it is almost certain that he knows of it through a personal experience/personal experiences. He seemed to me to be about the age of Littlefoot's grandfather. While I truly believe his parents have died long ago, I said "almost certain" as you never know if he went through the same hatching experience as Spike- no parents around. If he had parents to teach him, then that would still mean he had had the personal experience of seeing death. If he was born alone and learned from a stranger like Littlefoot, I doubt he'd have been so gruff with him at first. The again, if had the same experience, maybe the dinosaur he'd met had been irritable as well. He seemed very lonely to me, and a bit sad when he explaining to Littlefoot as well. You'd think he'd had a child or two at his age, so perhaps he/she/they died. In any case, I feel strongly that he has such wisdom from having seen it first foot. I am aware that my speculations don't help anything; I’m just an idle chatter.
I'd also think he was grouchy in the way he first spoke to Littlefoot, but that's just me.
Oh, I could speculate on the reasons for that all day. Perhaps he’d just lost his lunch to some rampaging dinosaurs like the as what happened to the gang. Perhaps he’d gotten in an argument with someone earlier. Then, we get to more “rooted” explanations, heh heh. Perhaps Littlefoot reminded him of his child/children if he had any, and perhaps if he did, he is now without. He could possibly not be a morning dinosaur, as I think it was early then. Perhaps he’s had one bad social experiences after the other, and just generally doesn’t like company. Again, I’m just wasting space.
Whatever the reason, I fully understand how his treatment changed when hearing of Littlefoot’s story. Same thing happens to me and I’ve seen it with many others in my life. You’re in a bad/irritable mood for some reason, so you lash out on anyone that passes by. However, hearing an unfortunate story can easily shift that mood. Sometimes I’ll be a poor mood. I come across as indifferent to people during those times. Then, say, I was contacted by someone who told me he or she lost his or her job. I would immediately switch to sympathy mode, and all but forget my prior feelings. My parents do the same thing. Also, this proves he wasn’t a bad guy, just having a poor moment. If he was in general a bad dinosaur, his likeness would not have softened after Littlefoot’s story. Sometimes we just need a reason to care. If he was a jerk, he would have blown Littlefoot off.
We don't know with absolute certainty if it was really Rooter from whom Bron is supposed to have learned about the death of Littlefoot's mother. Others would have probably seen the fight as well or later on her body, but this is just another possibility while that of Rooter being the one also makes perfect sense.
I think Rooter is the only one who comes to mind because he is the only we saw that knew of the incident. While it could have been anyone (as Rooter may have mentioned it to others who in turn may have passed it on until quite a few knew) I think it’s harder for the brain to automatically grasp uncertain possibilities when there is at least one that is known. If I give my forum password to someone, and my account is hacked, while there are a number of explanations we could think of, we’d already have a possibility we know about- the person I gave it to. Even knowing that Bron could have been told by anyone, every time I watch the tenth movie, Rooter still immediately comes to mind anyway, since he is the only lead that we know for sure exists. For one thing though, if the creators were making such a significant reference, as Rooter played a big, albeit short, role in influencing Littlefoot, you’d think the reference would be more workable, like:
“I heard from an old [enter Rooter’s species] that your mother had died and that he tried to give you some advice.” With the vague quote we have, we could wrack our brains for years only to continue the possibilities.
Lonely as Littlefoot was one might wonder why he did not try to follow Rooter (who could have offered some protection)
Perhaps Rooter had children and he failed to protect them, so he does not feel worthy to let Littlefoot come along. Perhaps he waited too long to have children and his mate died, if he had one. Maybe he decided not to have children but later when it was too late, he had regret for not continue the line of his herd, so seeing Littlefoot reminded him and in turn filled Rooter with regret. Not being heartless however, he gave Littlefoot some wisdom to travel with instead.
I don’t have any thoughts of my own on him, just felt like speculating on those of others.