Public vs. Private comments are confusing as the use of the term "Public" and "Private" does not align with it's use in other places within Hive.
"Public Comments" are visible to everyone within a project in our workspace including External Users, but not visible to people outside our workspace.
"Private Comments" are only visible to "Full Members" of the workspace.
However.. If go to the "...More" option to make an Action Card "Private" it is only visible to the people on that action card.
Most of our team thinks that "Private" comments are only visible by the people @mentioned in them.
A better solution would be to rename this toggle. Perhaps: "Visibility: Full Project Member / Visibility: "All Project Member"