Yes, it is only possible to access drafts created by other users if they have been saved in a space to which you have access. If the user saved the draft in his/her private personal content, you will not have access to it.
How to access drafts from other users?
When doing a search, you can
filterby 'states' and select
Users can grant your access to a specific Story
They can invite you to contribute to a draft (or a published Story)
Visibility of drafts from other users is particularly helpful for co-creation.