Yes,personal thoughts and observations can be racist, sexist, etc. I’d argue that our initial personal knee-jerk conclusions often are more profoundly erroneous in these ways because anything that makes someone feel uncomfortable almost always gets the blame as being “wrong”. And your response about not having evidence makes this point even more clearly. Absent evidence, we’re left with feelings, and those feelings are influenced by the media, etc. so, yes sir, you’re going to need evidence to justify accepting black people as the big bad ugly in society. And you’ll also need context. Let’s look at all of the stats around personal safety, tipping, etc, and really determine what you should be afraid of.
As for being Arab American, you say that as if 1) the poster implied anything about your race. All the poster said was about you being afraid of people darker than you. And 2) since when have middle-easterners been exempt from racism?