If one of your products says it has 1 tweet, that is a good thing.
It means that someone who has a twitter account added a link to your item to their twitter news stream. This means their friends on twitter can click a link that will bring them directly to your item. You may notice an increase in views to that item as a result. It depends on how many people see that person's twitter stream.
If you want to know more about twitter, check out the daily posts from the July bootcamp threads. Christine did an excellent job of explaining twitter and how it can be used as to increase traffic to your shop.