You have "Mention the author" activated but when your promo-tweet of the headline article was sent out, the @author was not included.
We are able to include the @author in your promo-tweet of the headline article if:
- we are able to find the information in the article's meta data
- there is enough space in the tweet to include it
- the @author has not requested a "stop mention" (a request to not be mentioned)
Note: This feature is not (yet) available when sharing an article manually (by using share button under an article).