What order were the wins and losses? The two big things that impact it are previous rank and order of wins and losses.
For instance, if the guy who was silver 3 went 0-4, then 2-0, then lost, then 3-0, mid bronze might be an accurate spot, and if he duo'd with someone in bronze and did that it def would be, because the first 5 games you play count for the bulk of your placements because they have the largest shift in mmr.
It works similarly to The way they do the computer administered GRE now days. The first questions in the GRE push you way up or way down really fast so the test can make your questions the right difficulty. Then it starts to give you questions that move you a little less in terms of difficulty once it figures out if you're on the high end of the low end. So if someone duo ques with a lower mmr player and loses a bunch of games to start placements, the game will assum they are worse than that and throw their mmr down there. Then if they win a couple but not all back to back, the game will adjust small and the wins in the last games will be like the difference between bronze 3 or bronze 4, but the large loss streak to start put them down in bronze and the game didn't match them against silver level players after that and just saw that they could beat bronze games and should be around there.
While I agree 9-1 should never be bronze 5, I also think that is because it should push the mmr faster in the first 5 games going up and allow for bigger drops in the next 5 if that happens. I haven't seen anyone go 9-1 and not go up a division unless they were bronze 5, and that is the only rank where your mmr can keep dropping and your rank can't possibly drop (at least this season, can't remember if that was true last season). They probably were never paired in a single game with a player higher than bronze 3 in that 9-1 streak and I think that is the biggest issue. If you go 5-0 you should at least get pushed to high bronze low silver mmr. If you go 0-5 then, there will be less issue with stuff bc a bronze 4 or five rating will be solidly justified bc you at least had a shot to play at the median mmr (50% point on ladder is like somewhere in silver 2 or 3 I think) and if you lose, then it feels less like getting cheated of the chance to move up.