What is confusing you?

In which part dba_admin's mesage contradicts my explanation?

I'm assuming the following part confuses you:
Originally posted by dba_admin
quote:
"If a system crash occurs, Oracle automatically restores the rollback segment information, including the rollback entries for active transactions, as part of instance or media recovery."
Automatically restoring the rollback segment information doesn't mean that oracle applies changes from redo into *empty* rollback segments, it applies changes to RB segments as they were in the moment of system crash. Consider the following sequence:

T0: RedoA is active redo log
T1: log swich occurs, data from RedoA is written to datafiles, including to RBS segments; RedoB becomes active redo
T2: System crashes. In this moment information from RedoB was not yet written into RB segments.

After starting the instance, oracle has to perform instance recovery. Before it starts recovery, the RBS segments allready contain information up to T1, so everything that was in RedoA is allready in RBS. During rollforward part of instance recovery the information from RedoB will be *added* to rollback segments. When this is finished, RBS will contain the information as they did in T1 plus additionaly applied information from RedoB. Finaly all the uncommited transaction will be rolled back.