Isovalue for volshow vs isosurface patch are different?

On the documentation page: https://www.mathworks.com/help/images/ref/volshow.html the isovalue must be a "non-negative number between [0 1]" if I use isosurface as the renderer. But when I use patch with isosurface I get a different result. Is the term isovalue subjective? e.g. does it mean a percentile if used in volshow?

Here: https://www.mathworks.com/help/matlab/ref/isosurface.html they use a negative value for isovalue.