Suppose Mr. foo and Ms. bar communicate each other in Twitter, and

1.If they use @foo or @bar in their Tweets, the others can reconstruct their time line, from their Tweets.
2.If they do not use @ and it is well known that they followed each other, then the others can reconstruct the time line,.
3.If they do not use @ and nobody know that they are following, then it may be difficult to reconstruct the time line by the others. Is that possible ?

In the 3rd case, Tweets may be able to use as a confidential communication between foo and bar, especially when they are not following each other.