Azure Failover Clustering vs On Premise Failover Clustering
Azure has two storage for 2 Vms; Traditional On-Premise contains 1 Shared storage.


Did you read The link you shared in the question, BTW I cannot see the diagram you posted in the question when I referred the link. I will quote from the same link.


  This article explains how to create a SQL Server Failover Cluster Instance (FCI) on Azure virtual machines in Resource Manager model. This solution uses Windows Server 2016 Datacenter edition Storage Spaces Direct (S2D) as a software-based virtual SAN that synchronizes the storage (data disks) between the nodes (Azure VMs) in a Windows Cluster. S2D is new in Windows Server 2016.


So the concept here is the two machines are using 2 different disk which is made as one disk and presented to FCI as single storage via Storage Direct Spaces technology.. Azure does not have concept of shared storage so you need some tool to present disks as shared storage to FCI. What it does is 




S2D synchronizes the data on the data disk and presents the synchronized storage as a storage pool.
The storage pool presents a cluster shared volume (CSV) to the failover cluster.
The SQL Server FCI cluster role uses the CSV for the data drives.
An Azure load balancer to hold the IP address for the SQL Server FCI.
An Azure availability set holds all the resources.