Native app design is in iOS or Android code
The code is packaged and must be downloaded and installed in the mobile app for it to run.
Native have their own version of “responsive design” via their respective codes. That’s why some apps accommodate portrait and landscape orientation of the mobile device.
Responsive web design is in HTML and CSS
The markup and style sheet must be uploaded to a web server then accessed by people via web browser.
Responsive web design is achieved thru CSS media queries, variable units (e.g., viewport width and height), and percentage (e.g., width and height in percentage of container’s dimensions).