Hello @Moin,
I’ve looked into this further. The posts showing in the user activity is only viewable to moderators (or those who have Trust Level to view). To me, this how it should be. It is not viewable to others from the users activity page.
However, anyone can use the search and target the user in a topic where a post has been hidden which will display in search results a snippet of the hidden post. A user doesn’t have to be logged in to do this.