Need MySQL configuration options like 'first time'
Encrypted passwords are stored in a table.  You apparently kept the data while updating the software?  So the pwd was still there.

You could change the password to nothing.
You could start mysql "skipping the grant tables.
You could live with the brief inconvenience.
You should consider moving forward to 5.5, 5.6, 5.7.  (With the same pwd issues.)