Note the question's user SmallestUncomputableNumber has over 1,000 reputation and this was their 23rd question. Also, why were there 2 first post reviews?
I gave an answer, with the top of its timeline showing
However, at the time, I already had over 620 answers and a reputation of about 18,000.
Note I checked the links to find all 3 of these reviews seemed to have occurred for those particular posts. Also, for comparison, the timeline of the other answer from Michael Stocker doesn't show any First Post review events. Also, my previous answer & the next answer to this one don't show any First Post reviews being done on either of them.
As for general details of what should be going to a First Posts review queue, a couple of references are this answer to the FAQ [What are the review queues, and how do they work?](What are the review queues, and how do they work?), as well as What are the criteria to be considered a "first answer"?, although the latter is from about 7 1/2 years ago.