ya. I think the above example illustrates a LOCK and not a DEADLOCK.

I think a deadlock would be encountered when session A is waiting for session B to complete something while session B is waiting for session A to complete someting else.

Try killing all sessions except that of oracle
SELECT sid, serial# FROM v$session WHERE username IS NOT NULL

and ALTER SYSTEM KILL SESSION 'SID,SERIAL#';

and then retry truncating the table.