Just don't understand.........

I really don't understand some people...actually most people for that matter...

Why do people really want to teach their kids to be vindictive or even to hold a grudge...especially at the ripe young age of 6?????
Ok to elaborate on this story....There's this little girl that lives in my court and she rides the bus with my kids and is in my youngest sons class. Well the other day, as they ran home from the bus stop my middle son some how tripped her as they ran. So she fell, and was understandably upset that her knees got dirty from the fall. (this girl plays as rough as the boys on any given day and usually out runs them in any race.) So of course an apology was in order, made and all was done, everyone seemed to have moved past the whole incident.
The following morning at the bus stop, which I always walk my kids in the mornings....this little girl, comes to the bus stop in tears. I had and still have no clue of why she came to the bus stop completely in tears.
Well she comes straight up to me, so I ask her if she was ok, she says no and begins to bury her face in my jacket while crying at the bus stop. I stood there consoling her, asking if she had just gotten in trouble while getting ready for school, if she wanted to talk about what was wrong ...all her answers was no. So after a few minutes, her mother begins to drive out the court on her way to work. Her mom stops and asks why she is crying, and she yells in this loud burst that she was tired. Then her mom looks at me, then each of my boys, and says "her pride is hurt from the fall yesterday"; completely out of no where. Then this little girl, turns her back to me and the boys. Her mom then leaves and I look at the girl, and say are you really still mad about that...she says yes. The bus comes and I give my boys hugs, and she turns to me, then gives me a hug before she gets on the bus....My son said once they got to school she was talking to him as if nothing happened.
So can anyone explain to me, that while I'm the one consoling this womans child, for what ever reason, as this woman rushes off to work, is she trying to cause a rift..when their obviously is none, where me and my family was concerned????
Also, this girl is usually at my home within 15 minutes of getting off the bus everyday, wanting to play with the boys, and has not shown up at the house nor the bus stop since this day???

What is this about?
Should I had just sat there and watched this 6 year old child cry until the bus came?
Maybe they're embarrassed at what they think the girl may have revealed to me? (I did notice that while she was on her way out of her house that her grandmother seemed to be having some intense words at her....) but I never mentioned this, if she wanted to talk about it, she could have, but that wasn't my business....right?

I don't know I just don't understand...............