Pretty much every change that goes into production should be looked at by at least two sets of eyes - the dev who writes the code and a second person to review and approve the pull request. Some orgs will require multiple PR approvals before shipping code, that would vary by internal policy.
I guess the tricky thing about this bug was that it only appeared on maybe 1/6 page loads from my testing, and only briefly appeared for a second or two. You also needed to be logged in with your own account to see the other person's details. (otherwise you'd just get the generic "Login" button) It shouldn't have been missed, but I can understand how it may have been.