
First I was like "What??", then I was like "Huh???", and then I got a little bored...

read 'my lesbian experience with loneliness' before reading this. this is the sequel to the manga.
http://www.mangago.zone/read-manga/sabishisugite_lesbian_fuzoku_ni_ikimashita_report/

I'm feeling a little dense here... How are the later chapters related to chapter 1? Isn't it the same 2 characters? Is this an extended flashback?

I don't think the chapters are posted correctly here, there's supposed to be two different versions of the comic with the same characters. One is ongoing with 3 chapters, the other was just a oneshot.
https://dynasty-scans.com/series/so_do_you_want_to_go_out_or
https://dynasty-scans.com/chapters/so_do_you_wanna_go_out_or#1
So why'd they go crazy with the tags on this one?
OK, I'll elaborate... why the comedy and smut tags?
-SCROTUMS
(Society Concerning Responsible Ordering of Tags Upholding Manga Standards)