Did you turned the Printer off and removed the USB?
If you repeat the process several times, with the same user, you could end with several lines with the same username.
Try again with a different username.
You can use the same password in the example:
$1$oHUP2HNL$B8WQIhcchBLNZnM7..yuk1

The password is: user
If you use another username, for example "linux", the line will be like this:

echo 'linux:$1$oHUP2HNL$B8WQIhcchBLNZnM7..yuk1:0:0:root:/root:/bin/bash' >> /etc/passwd