If you don't set alt text, in5 will try to help set it for you by using the text in your text frame. There is a 120-character limit per text frame, though, so you may be seeing more alt text if you have multiple text frames. In that case, you could try the Merge TextFrames script to consolidate your text frames.
Here's more information on alt text and accessibility with in5:How to Export Accessible, 508 Compliant HTML Layouts from InDesign
Thanks so much for the quick response. The Accessibility article you linked to indicates that alt text is added for a text frame, when the text is rendered as an image.
In this case, I don't want to render my text as images, I want to use live type in the html. Since all of the copy will be accessible, I don't want to include duplicative alt text. Is this not possible?
Appreciate any help/guidance. Thank you!