Using a human host was just an example to show there are certainly real possible applications whe magnitudes of these units is useful. DNA-based data storage doesn't necessarily mean humane genome data - you can store any data (1) in a DNA strand and the strands in a container could all be unique datasets. Possible, albeit not yet practical - but to discuss the realm of the possible you still need appropriate units, and TB/ns seems to be appropriate for such an application.