Both your claim and the parent's claim are equally shocking, and the evidence for both is hearsay from someone who lives on the street. How do we know who is being sincere, who is pushing an agenda, who is mistaken, who is experiencing cognitive dissonance, etc.
I think there could be an aspect of availability heuristic. You don't watch news of police not acting aggressive towards protestors. That doesn't mean it doesn't happen, or doesn't happen even more often than it does. Same with the comment below about why cops aren't speaking up. I've read some articles where they are, but again... it's not going to make news nearly as much as the bad apples do.
This doesn't negate the bad apples and all the bad things that have happened or in any way go against the protests. Just try to be aware when classifying an entire group as bad based hand picked information presented to you.
Of course there is that history. But there are also people who paint the police in an unwarrantedly bad light. People tend to forget that humans are overwhelmingly cooperative and good. Society would not be as stable as it is if people were as consistently bad as some people make them out to be. There are ideologies misrepresenting reality on both sides of this situation. It's so hard to concretely say anything in these situations without examining all the context available.
Well, if the police are overwhelmingly good, where are the representatives of the police unions that are condemning the “few bad apples” that are killing unarmed Black people?
Where are all of the “good policemen” who are saying racial profiling during “stop and frisk” is wrong.
If they are complicit and silent they are not “good”.
And I bet you have never been thought of as “suspicious” for walking from your house down the street to your mailbox.
