First of all, no, you should not downvote duplicates just because they are duplicates! Duplicates are useful because they help direct users to the right answer. The search functionality of the site is, um, well, less than perfect. It is not easy for experienced users to find dupes, let alone new ones. So no, please don't downvote dupes just because they're dupes¹.

That said, yes, the review system is flawed. Remember that this is automatic, it simply selects upvoted questions and considers them "good". Sometimes, sadly, we have bad questions (although I don't think this is an example of one, it seems perfectly OK to me) that are nevertheless upvoted and sometimes those make them into the review tests and make people fail the test for selecting the right action. Don't worry about it. Unless you fail a lot of tests, nobody cares. And even if you do fail a lot, that will just ban you from review for a little time. After that's over, you can come back and review again.

¹_{OK, there are some cases where the duplicate is so easy to find that it shows the OP clearly put no effort into the question. You can downvote for the lack of effort, just not only because it is a dup please.}

First of all, no, you should not downvote duplicates just because they are duplicates! Duplicates are useful because they help direct users to the right answer. The search functionality of the site is, um, well, less than perfect. It is not easy for experienced users to find dupes, let alone new ones. So no, please don't downvote dupes just because they're dupes¹.

That said, yes, the review system is flawed. Remember that this is automatic, it simply selects upvoted questions and considers them "good". Sometimes, sadly, we have bad questions (although I don't think this is an example of one, it seems perfectly OK to me) that are nevertheless upvoted and sometimes those make them into the review tests and make people fail the test for selecting the right action. Don't worry about it. Unless you fail a lot of tests, nobody cares. And even if you do fail a lot, that will just ban you from review for a little time. After that's over, you can come back and review again.

¹_{OK, there are some cases where the duplicate is so easy to find that it shows the OP clearly put no effort into the question. You can downvote for the lack of effort, just not only because it is a dupe please.}