Preventing Spammy User Accounts
If it's a small wiki and you know the people editing you could just ask him. Or ask on his talk page, but I agree: If this is a public wiki and ithere are no anti-spam measures set up, these two users might well be spammers.
To avoid spammers registering in your wiki, you can set up the Extension:ConfirmEdit, which comes with MediaWiki 1.18 and newer. It allows you to show your users a captcha when they register.