Chart Viewer is a static website. Everything it does with your data happens in the browser tab you are using.
Files you choose, drop or paste are read by the browser and charted on your device. There is no server that receives them and no account that could link them to you.
Everything stays in your browser's own storage. Your open files are kept there so they come back on your next visit (up to eight tabs and 10 MB per file), together with preferences: the interface language, the theme and style, and the last chart chosen for a set of columns. Turn off "Remember open files" in the header, or use "Close all and forget", to remove the kept files.
PNG, SVG, HTML, PDF and CSV exports are created in the browser and saved straight to your device.