You could have answered this question yourself had you done a bit of research.
Your understanding about a distributed set up is correct. You have database on node 1 and SAP on node 2. Whereas the HA (High Availability) environment basically means that you take care of the components that can cause the SPOF (Single Point of Failure) with maximum up time.
From the installation point of view a distributed setup and HA setup can possibly look the same. The difference here is that you make use of a cluster software in the HA environment. The cluster software is provided and licensed by the OS vendor. Eg: HACMP for IBM AIX, MSCS for Windows.
In a distributed environment if the database or SAP (CI / PAS) crashes then there is no failover.
In a HA environment if there is a crash of the database or SAP (CI / PAS) then the system will move the failed node to the second node.
If there is no cluster software involved then there is no HA. In the event of a crash (DB or CI) you will have an outage until you start the failed node after correcting the problem.
Regards
RB