Thank you so much for your question. If you missed to add featured image on that page, Alt tag will appear so that about is appeared there.
You can get rid from this with two method.
1. Add the featured image on that page. Look here to add the featured image.or,
2. You have options to hide the featured image. Edit that page and scroll to bottom and in Other Option section, you will get the options to hide the featured image. Select on Hide the featured image and it will disappeared there. (In case of you don’t want featured image on that page)
Hope, this will solve your problem.