Pshem, I think can see where the confusion is coming from.
Points are real world units, as are inches, millimetres, etc. Pixels are not real world units.
Pixels only exist in the computer. A raster image is made up of a grid of pixels which are indivisible elements of the image. A pixel in an image has no inherent size; it is just a unit of information which tells the computer how that small part of the image should be displayed.
An A4 page is - as you said - 595 points wide by 841 points high (give or take) however, in itself, it has no Dots Per Inch (or Pixels Per Inch) measurement. It has a size but no resolution.
Every image is stored with a recommendation as to how it should be displayed. This is the DPI (or PPI) of that image as it exists in the file (this is important to note). If an image has a DPI(PPI) of 72 then it is saying that it should be displayed in a way that 72 pixels should cover one inch. In other words, a 72x72 pixel image at 72DPI(PPI) should be one square inch in size. (The size it will actually be on your screen depends on many things that are outside the scope of this explanation.)
If, as you have said, you have an image that is 4960x3508 and that image has a stored (on the file) resolution of 300DPI then that image will - when put in an image frame - be 4960/300=16.53 inches wide by 3508/300=11.69 inches high.
If you put this image into an image frame that covers your A4 page (which is 595 points x 841 points in size, which works out at 8.26 x 11.68 inches - at 72 points in an inch) then the image will be about twice the width of the image frame while the height will be about the same.
If your image was 72DPI rather than 300DPI then it would be much larger than the image frame (or page) at 68.88 inches wide by 48.72 inches high. (This would be "crazy huge".) On the other hand, if your image was 3000DPI then it would be just 1.65 inches wide by 1.16 inches high, probably way too small to make out any details.
By default, Scribus always displays images in image frames with deference to the resolution which is stored in the image file unless you have the image scaling set differently in "Preferences (or Document Setup)/Tools/Images".
However, if you select your image frame and go to "Properties/Image" you should see the "Actual X/Y-DPI" values. If the X/Y-Scale values are both 100% then the Actual-X/Y DPI will be whatever was stored on the file. If you change both the X/Y-Scale values to 50% the Actual-X/Y DPI values will double and the image will be displayed at quarter the size. Conversely, making the Scale values larger will make the DPI values smaller and the image will be displayed larger. Scribus can only display images at the resolution that is set in "Properties/Image".
Larger scale = lower visible resolution (DIP/PPI) and smaller scale = higher visible resolution but that's just the resolution of the image as it's seen on the screen or would be printed on paper. You don't actually change the resolution of the image itself, you only change the resolution of how it will be displayed/printed.
The thing to keep in mind is: Pages don't have a resolution/DPI/PPI but images do. A page has no concept of a resolution, it is just somewhere to put images that do.
I hope this helps to explain things a bit better.