It took me a little research to figure out what you're doing. When you use Live Caption, you're pulling metadata from the file. Metadata is defined in a format called XMP, which was developed by Adobe. You can view metadata best in Adobe Bridge. If you select a picture and view the Metadata panel, you can see the metadata that's in file. In Live Caption setup you're apparently picking the "Dimensions" field, which is defined in pixels. There is another potential piece of metadata (Dimensions in Inches) but it is not filled in in the JPEGs. To figure out how to add a metadata field that is not in the file, you'll have to research how to edit XMP metadata. There doesn't seem to be a mechanism for editing that field in Adobe Bridge.
There's nothing in InDesign that would allow you to edit the field. Maybe someone could write a script that would edit the caption after it's in InDesign, and convert it to inches.