Fiji is correct, the volume itself is 16-bit, but it contained 8-bit values only, and the example encoder knew about this.

Now there's a PackWHSRatV4Demo.java file too.

Looked at the inia19 dataset, and generally it will work with QuickNII, as the most important restriction of QuickNII is the isotropic voxel size. Smaller hiccups are expected though: the label file format is different from ITK (so a modified parser is needed), and the orientation is LPI (axis order matches, but all axes are in the opposite direction compared to what QuickNII will display).