There are two points which distinguish a post from a comment:
1) For comments, a message balloon (blank) is displayed in the item box. In addition, the message is shown as follows: "from among x comments".
2) For a post, Scup displays the following in the item box: "With x comments".
After having identified a comment in the Mentions tab, you can find the related post as follows:
In some Facebook mentions, you will see the context together with collected item.
This works for comments, private messages or replies and shows up to two context levels. However, the context will only appear if the previous mentions have already been collected by Scup.