Q: "Other" login

Not that I am aware of. How would I have done that?

Guest User has been off. That's not it. But thanks for your reply.

Not solved.

I see no way to disable Root User as instructed in step 9.

I just don't see the option "Disable Root User" (step 9).

Nope. I don't see Enable Root User either.

Maybe I'm not doing the correct thing. When I go to Users & Groups, I see Login Options, then at the bottom I see Network Account Server: and the "Join..." button. Hitting that, I see Server: (I don't know if I have to enter something or not--I've been leaving that blank). Below that I see the Open Directory Utility... button. Then I see on the top: Services, Search Policy, and Directory Editor. If I select Directory Editor, I see "Viewing" with a lot of options, but I am presented with "Users"; then "in node" with "/Contacts", "Local/Default", and "/Search" (which is presented). Below that I see a list of 113 items, from "_avipm" to "WWW Proxy". The words "enable" or "disable" do not occur. I'm not at all sure if I've done what the instructions call for (from March 2015 -- may not be applicable to El Capitan.) I decided to look for more info in Apple Support, and I got a message that I have a trojan virus -(e.tre4456_worm_osx) on your Mac. Press OK to begin the repair process. This led to something from Mac Cleaner, which found 1188 problems. They wanted me to pay $40 to download a  different version of Mac Cleaner to fix the issue. This seems suspicious to me. I am currently scanning the computer with Avira.

Okay. I see the option in the Edit menu to Enable Root User. So that tells me that the Root User is not enabled. Then the "Other" option on the login screen is due to something else.