If in Preferences you have set the Unit to centimeter, than your texture import is measured in centimeter (as indicated).
If in Preferences you have set the Unit to meter, than your texture import is measured in meter (as indicated).

You can only set width or height, not both. The second value will be calculated by SH3D based on the proportions of the image.

Do all textures you try to import have the same problem? Or does the problem occur only with this specific texture?

Hans