I took a look at the data. Everything seems to be fine; Matlab's values match AFNI's values. The BrikLoad function scales the data applying the scale factors if necessary, so you don't have to worry about it. The scale factors are fairly typical to scale a short integer down to a floating point value. If you don't want to have scale factors, you can convert the data to float with 3dcalc -datum float -nscale. To verify any particular voxel yourself, you can set the AFNI gui to display voxel coordinates instead of xyz position in the Define Datamode, Miscellaneous menu. Note the i,j,k coordinates in the upper left and the voxel value in the Overlay panel. Alternatively, you can use 3dMaskdup -ibox i j k dataset+orig'[19]'. Then in Matlab, do something like

>> V21(32,65,4)

ans =

2.0449

Again, keep in mind the coordinates in Matlab are 1-based so add 1 to each of AFNI's coordinates (i,j,k,sub-brick).