I don't know what made your Terminal window lose the focus on your first attempt, but I'd bet that Control-C stopped the dd process the second time, and the Option key was extraneous. I ran the command you referenced in your initial post and stopped it by typing Control-C; this is my Terminal transcript:
$ sudo dd if=/dev/rdisk0 of=/dev/null conv=noerror
Password:
^C3359+0 records in
3359+0 records out
1719808 bytes transferred in 3.897634 secs (441244 bytes/sec)
Other than a different set of numbers, adding Option to the key combo yielded the same result.
That caret/capital sequence is the symbolic representation of the Control-C key combo, which always shows up in Terminal's output when you use it to stop a process.
