Here is what i had:
1. What is the free space available on datastore before cloning the disk and after cloning the disk? If there is not change in the space then the disk created in a thin disk.
2. Which datastore are you using. If it NAS datastore,is it a VAAI-NAS feature supported volume?
3. Did you observe the disk type as soon as it is created/cloned from the command that you used or after attaching the disk to VM? Please observe the disk type before you attach the disk to VM(just after adding and before clicking "OK" radio button to complete the disk addition task) from UI and after attaching the disk(after clicking the "OK" radio button) in UI