Is this good for the start of a short story? (don't worry, it's short)?

What you write after this beginning obviously depends on where you want to go and what you want to say. The opening, while effective, is very casual, and by the second paragraph you are already moving in a different direction. You seem to be improvising as you move along, without a plan or an organizing theme. Ask yourself this: How is the story going to end? When you have decided upon that, go back to the beginning and decide how you will get from A to B, so to speak. Then you will have something to guide you, and will be able to answer your own question - namely, is what you have written a good beginning for your story.