That is interpolation as they are scaling the image up. increasing megapixel count requires the sensor to shift in multiple directions in order to allow the camera to better analyze the light that is coming through the lens, and thus get more detail. Since pixels are larger than a photon of light, when you take a photo, you will end up with multiple units of detail hitting a single pixel on the sensor (e.g., 2 grains of sand on the beach close enough that their light photos both hit the same pixel, and thus you can see both grains in the final image. by moving The sensor around and allowing those pixels to sweep across the stream of photons, the camera can do some processing inn order to effectively increase the resolution.
This is a function found on some expensive medium format cameras in the $30,000+ price range. (for it to work the camera has to be perfectly still, any movement in any direction greater than the length of a pixel on the sensor, will ruin the process entirely)
With a fixed sensor, the most you can do is take multiple frames, and then stack them, then take the men of each pixel. This improves detail and color accuracy by effectively improving the signal to noise ratio.
You can do this manually in photoshop by setting your DSLR to lock the mirror up to prevent any movement, then take like 10 photos of the same object.
then bring the images into photoshop, then stack them all as a smart object, then change the stack mode to mean.
Since the noise and other unwanted elements in an image, are random, but with in a certain number of standard deviations of what the pixel should be, too the more images you stack, the closer you can get to the true value of the pixel, and pretty much get to a noise free image with better color and more detail. While this will allow you to enlarge am image further, it is not increasing the resolution of the image, it is just bring out more detail in the resolution. for example a 13 megapixel image from a smartphone will have less detail than a 12 megapixel DSLR.
No amount of stacking in this method will get you more detail than what a perfect 13 megapixel can give, but the more you stack, the closer you get to having detail that matches the number of pixels. (at least until you hit hit the limits of the lens
(for many cheaper cameras, the the imperfections in the lens, are larger than the pixels on the sensor, and thus you may end up with a camera and lens combo where the sensor may be 13 megapixel, but the lens may only be able to let through 6-8 megapixels of actual detail, in which case, no amount of stacking will get around that issue (and you cannot move the camera as that will change perspective)