Hi Vinodh,
I have tested the similar scenario on a test website with AAM and Target.
I have implemented AAM and Target using DTM. I have a number of segments (more than 10) that are created from rule based trait.
I created an A/B testing activity in Target, and I did not choose any AAM segment, and I just proceeded with default : All Visitors.
Now when I visit the website page and run mbox trace, I see those AAM segments for which I am qualified, so I saw 3 segment IDs in the mbox trace. (for those 3 segments the condition was to just be a visitor of the site)
Then I created another AAM segment using rule based trait, and got qualified for it. Now I see that 4th segment as well in the mbox trace logs, and so far I have not linked any segment with that Target activity.
Apologies for my limited knowledge in previous response about segments in mbox trace logs.