There is no reason for DB to hung in what your firend did. May be your online redo is large and DB was taking time in instance recovery. Or may be the shutdown was not clean & complete. You may have such problems if the shared mem & semaphores are not cleared. Try ipcs & icprm ( carefully).
The procedure of starting & stoping archiving is through thsi init.ora parameter only so what he did is right.
I am not sure if I understood Suresh's posting clearly or not. However as I understood what he wants to know is "how to turn off archiving WHILE import is GOING ON".
Having said that, when Suresh said that the init.ora file was modified and the DB bounced, I assume that it was done with the abort option (otherwise it can't be done right? the import is still going on!).
So, the the DB was restarted, oracle was doing instance recovery (must have been a large table which was being imported) and so it seemed that the DB had hung.
As far as setting archiving off, Jeff has already pointed out what to do.