Nutanix snapshots are pointers in the metadata pointing to a specific time. Snapshots are created verry fast and all the data will stay on the cluster. Snapshots can also be copied to another cluster (data protection). 

Backup is done via third party tools. Backups are…. backups You can restore/place backups on all kinds of media/locations. If you want to play with an easy to use backup solution try looking ad HYCU. 

And and to make it even more complicated, backup tools will also make snapshots ;)