Yep, and I am happy to use "they" in that setting. The Stanford rules are silly because they also call for using "they" to refer to people whom you do know, if they've never specifically instructed you on their preferred pronouns. I am apparently supposed to refer to President Biden as a "they", since he's not told me otherwise.
"Someone ate the last slice of cake. I wish they had considered me!"
"Phone for you" "What do they want?"