Hi Jae,
The initial "Data linked to the filtering dimension" can be considered as a category to differentiate it from the other options here which are totally different (external data, offer, link).
Then you have to finetune that choice by specifying if you want actual data of the filtering dimension (fields), or linked data (fields from tables related to this dimension).
As a side explanation, this is an historical label, and at the beginning Adobe Campaign was... coded in French, then translated into English. Since the first time this feature was added, it stayed that way.
The first term is simply seen as a overall category, even if the same one appears again after that.
I'm sorry if that confused you in some way and I hope it is clearer now.
Let me know if you need more clarifications,
Florent.