Based on this answer by PirateEric♦,
If it's anything like 2007, the membership aspect of My Sites is
worthless. In 2007, it required that you explicitly be entered into
the Members group in a site/site collection. Anything higher (like
owners or designers) you didn't show up. Anything lower (like
Visitors) you did not show up. If you were given direct permissions
you did not show up.
If you were in an AD group that is added to the sharepoint members
group, you will not get a membership entry on the mysite. Only the
direct add of the user account DOMAIN\username will fill the
membership, if added to the sharepoint members group.
How does Membership show in Mysite - SharePoint 2010?
does the Membership tab only show users who were added to the original
'members' group or will it also show users who have been added to
other permission groups which have a 'contribute' permission level set
on the same site?
It will only show users who were added to Members group.
You might also notice that Security Group Memberships are not shown.
They are, however, displayed in the Newsfeed:
Memberships in Sharepoint 2010 User Profile