If your images were included in your Word file when you imported to Atticus, it is likely that Word added automatic descriptions to the data which was then interpreted as captions by Atticus.
To disable this feature, open Word and go to File > Options > Accessibility. Look for the Automatic Alt Text section and deselect the option that says "Automatically generate alt text for me." Click OK to save your changes. This action should prevent such descriptions from being added in the future when you import documents into Atticus.
If you would like to remove the captions within Atticus, you can click the cog icon near the top right corner of the image to open the image options. Here, you can remove any text from the Caption field.