Unless I'm mistaken, the tbz value is supposed to show the number of blocks not being zeroed yet. However, this value will also be zero in case of a newly create thin provisioned virtual disk. Are you sure the vmkfstools -D output is from the correct .vmdk file? To me it looks like this is a thin provisioned virtual disk on either a VMFS3 datastore with an 8MB block size, or an upgraded VMFS5 datastore.
André