Typically, Google will not show star reviews in your local listing in the Google search results unless you have several reviews. If you have one review, Google will typically just not show the review or star rating. But Neal Resnik spotted and posted on Twitter an example of a local listing in the local pack with one review and Google showing stars.
Here is a screen shot:
Neil said "today must be a testing day at Google. Here's a star rating for a business with one review." Joy Hawkins also posted about it on Twitter, citing Neil and overall, it confuses the local community.
Maybe this is an example of there use to being more reviews and then some of the reviews drop but Google keeps the ratings? Maybe not? I am not sure.
Forum discussion at Twitter.