There are a couple of reasons I'm finding this difficult to understand.
First, they explicitly ask about different things. The first is about documentation comments, and says:
This is not a question about in-line comments.
And the second says is about in-line comments and says:
(ie, not javadoc style method or class comments)
As a result, both questions have answers- including the accepted answer for each question- which would not be a valid answer to the other. The accepted answer to the closed question, for example, is about expressing a method's intent through it's signature, which would not have made sense on the other question.
Second, the "Comments are a code smell" question has been closed as not constructive and locked as only existing because it has "historical interest". My understanding was that the choice of which question to mark as duplicate isn't just about which is older, but which is the better question. For example, the help center describes one function of questions marked as duplicate:
but often they are left as a signpost pointing people towards the canonical answer to that question.
Given that, it seems bizarre to close a good question as a duplicate of one that would have been deleted if it weren't for "historical interest". Does it make sense to have a signpost pointing to such a question?