What is the likelihood of a dog attacking someone whom is paying no mind to the dog and has their back turned to it?

I was attacked by a dog yesterday who was being walked by her owner. The dog saw me standing there when she was walking up the street towards me and she didn't seem bothered by me at all; just going along her merry way, then as soon as they walked behind me she just snapped and jumped at me. Her owner pulled her off with the leash and the dog was just sitting there as if nothing had happened and I didn't matter. Her owner just kind of said without much shock that "she's never done that before," and suggested it must have been he color of my clothing.

It just seems odd that I was attacked and I haven't been able to figure it out. Any thoughts?

Very off, may have been a odor or clothing blowing in the wind. Or the dog may just be mean.

Were you moving? Many dogs have a "chase" urge. Odors and startles are a possibility, too, as Chuck says.

If you are acquainted with the owner, you could get paranoid.

Unless you anticipate seeing them again, I wouldn't worry.

I'm very sorry to hear that. I hope you are OK??

It's not very likely that it would happen again.
We had a Great Dane years ago that didn't have very good peripheral vision, a boy (he was 16 at the time) was visiting from next door and was crawling on all fours on our floor in front of the dog to get something from under the coffee table... the dog didn't know it was a person and bit him on the head.

The boy didn't blame to the dog at all which we were thankful for and the dog never hurt anyone ever again...