Does That Make Me Racist?

I've been seeing a lot of posts lately claiming that white people are born racist.  I always thought this was nonsense.  The way one is raised determines what they believe.  And then I thought about an event that had occurred in my life.
One summer night, a little before midnight, my older sister and I were driving a friend back to his home.  He lived in a rough neighborhood with a mostly black population.  After saying our goodbyes, my sister and I headed home.  While still in the neighborhood, we drove passed two black teen boys.  One of them jumped on our car and then slipped off the other side.  This event really freaked us out.
Arriving home around midnight, we pull into out parking space and witness a black women walking into our home.  Again, we were a little freaked out.  But why were we so distressed?  Would my sister and I have acted the same way if a white woman were walking into our house at midnight?  Honestly, I don't think we would have.  We would have been confused, but probably not worried.
After warily walking into the house, my sister and I found our next door neighbor, who was extremely pregnant, with my mom in the basement.  She couldn't sleep and wanted to see what we had done with our basement.  This woman and her husband, both black, were the best next door neighbors we had ever had.  My sister and I both felt very guilty for assuming something bad was going to happen.
I am not racist.  My sister is not racist.  No one in my immediate family is racist.  I think that my sister and I were still stressed out from the teen boy jumping on our car.  Because of this stress, seeing a black women walking into our home made us a little cautious.
I hope no one thinks any differently of me (or my sister) because of this little blurb of an event.  This happened probably twelve years ago, but it's still on my mind to this day.  It bothers me that I judged such a wonderful woman based on someone else's actions.  My parents were very firm about teaching my siblings and I to love our neighbors.  Not just our literal neighbors, but those who we see in our everyday lives.
I don't offend easily, but those posts claiming that (to a certain degree) all white people are racist really upset me.  It's like I'm being accused of a crime I didn't commit.  I am not a racist.  A person is a person, no matter what they look like. Treat everyone the same way.  Love everyone.