That would certainly make sense for #1 and #2 . A little odd since it was a 1x1 F on the A321 but I can see #1 and #2 wanting to be upgraded together, especially if they were sitting next to each other in J or Y. Given it was sold as a 2 class plane 4-7 might have already been in J (as I was) and #8 might have been the first person it made sense to upgrade from Y to J. Sadly, I didn't see what seat #8 wound up in.
Since this flight is sold as two-class, as you pointed out, the Y and J cabins are treated as Y for the purpose of upgrades. There's no such thing as a Y-J upgrade, or a J-F upgrade being treated differently from a Y-F upgrade. Rows 1-5 are F, and rows 6-22 are Y.
Now, it does seem like 1 and 2 on the list were traveling together and did not want to be split up should only one upgrade become available. Not sure what gives for 4 through 7 on the list--most likely scenario is you had a lousy and/or incompetent GA who, when said pax did not respond to her pages for the upgrade, simply skipped over them and gave the upgrade to the next person who responded (in this case number 8).