That message comes from the rule where for non-core infrequently-used functionality, an app need not disclose the data collected if it is not used for advertise or tracking, it is clear and obvious what data you are collecting, and you clearly show the user id as a form field.
For example, if your feedback form allows users to optionally enter their email address so you can contact them to request more details if needed, you don't need to specify that you collect email addresses if you never otherwise collect email.
It is not clear if this would also apply if users can optionally upload a profile photo, but profile photos are not a core part of the app (e.g. not a tinder clone). If it does apply it would let you omit the scary sounding 'user photos' option from the privacy list.