XF 2.3 How can a member change their month/day of birth?

[mjda]

I have a member who registered way back in 2017. Recently I was browsing the user change log and I came across this entry for him:



My question is, how could he change that? I, as a super admin, can't even change my own birthday. When I'm viewing that page I see the message "Once your birthday has been entered, it cannot be changed. Please contact an administrator if it is incorrect.".