This is the best analysis of the situation I've seen yet. Thank you!
You're exactly right: many things can be true at the same time. Amy Cooper had good cause to be very worried about her dog, but her actions towards Christian Cooper were pretty clearly racist and unacceptably dangerous for him (even if he wasn't black, even if she wasn't a woman, but all the more so given that they were who they were!). And Christian Cooper can have been acting like an asshole, as you put it, and still have been a target of racism in the response.
("Both" can be true of dogs, too, which is what prompted all this--dogs can be frightening, especially to children; annoying or messy; occasionally dangerous--leash laws aren't just there to annoy dog owners. AND dogs can be lovable, loyal, nearly as dear to people as their own family members--so threatening an owner's dog is not something to take lightly.)
The one thing I would add to your "There are just people." comment is to make explicit that people, if not their actions, need a chance for forgiveness.
This time, nobody died, thank goodness. We can take a break from demonizing and polarization, and encourage both people who haven't acted their best to reflect and do better next time. (Not that the two actions were comparable..."I will do something that may get you killed" is a substantial escalation on "I will do something you don't like to your beloved pet".)