Sounds like Flexi is just using screen resolution for its display of the JPG. Resizing can be done without loss of resolution providing that the pixel dimensions remain unchanged. I'm not sure if resizing in Flexi will do this or not. In an image editor, which Flexi is not, such as Photoshop, resizing provides the option of resampling or just changing resolution. Resampling changes the pixel dimensions and changing resolution does not.
To state what I am trying to explain differently ...
An image measuring 1500 x 1500 pixels (the pixel dimensions) is 10" x 10" at 150 pixels per inch, 5" x 5" at 300 PPI, and it is 20" x 20" at 75 PPI. The absolute way of describing an image's size is in pixel dimensions.