Where did this guest account come from?

Returned to game after closing browser. Says “sign in” but I’m able to enter a chat message. Also, I can enter a private message. Then I realize that it is Guest88388 who entered it. That is a nifty way of creating a logged in guest! This guest also was able to bring up my profile and apparently was about to send me a game challenge before I decided I didn’t want to play myself. Oddly, although this guest could enter text into a private message, the Send Message and Add Friend buttons were not responsive. Strange.