Why could a dog howl at me?

I was walking pass a group of friends of mine who were playing with a dog (I really don't know what sort of dog was he). Just as I came up to them, the dog started howling at me and he became kind of scared (I guess) and started whining a bit and then I got away. It really bothers me because I read that dogs react to negative energy and it makes me think that I was a source to it. I read all sorts of superstitious things that dogs for example foretell death if they howl. I know there are enough rational reasons for them doing so but its still scary if it happens to you.