Hi @Melissa_Heuer, welcome to the Asana Community Forum!
If the task is not added to any project, it will be private to you (as the creator) and it’s collaborators. When you see “This task may be visible to additional people.” is because the task has collaborators that can also access the information in that task.
If you see “this task is in a hidden, private project.” is because the task was also added to a private project. My hunch is that one of the collaborators added the task to a private project. Please note that even if you create the task, the collaborators have the same level of access.
As a workaround, if you don’t want them to edit the tasks, you can create a private project and make it comment only. Please make sure you are the only project member. Then you can create tasks and add collaborators and they will have comment only access.
I hope this helps!