Key words: "Add a picture to help people recognize you".
Your current profile picture may help friends and family recognize you, Fair enough.
However, if the profile picture is not a photograph that GMail can recognize as a face recognition person then that may have triggered the message.
Otherwise, as above, could simply be some bug.
Check your account and if all is well then just ignore the "prompting".
Unless of course you do want your recognizable face to appear.....