Hello Se Je,
The option on Tableau Public for data download includes the option to download the workbook. You might consider disallowing this option and then creating a view which shows the desired data that can be printed out from a browser as an image.
The best way to handle this requirement is to have the end user of the dashboard/worksheet open the View Data window for the viz and then use the download data link from that window. This window is fully accessible (i.e. conforms to the WCAG 2.0 Level AA guidelines). You can find more information about designing accessible views as well as the keyboard shortcuts for interacting with vizzes and opening the View Data window in the Tableau online help here: