I’ve seen something like this where another ambari schema was created somehow and ambari.properties was pointing to this new schema.
Checking hosts table is not a good check to see if you have your original data still, because ambari-agents could have heartbeated in with the ambari-server to populate the hosts table (hosts get populated independent of any cluster existing).
You can check the other tables as suggested. Also check the output of /api/v1/clusters and /api/v1/persist.
Also check /etc/ambari-server/conf/ambari.properties’s server.jdbc.database_name property to see if it points to the right schema.