Wowza this post, like most others, got off topic. Anyway, It's probably bc Rito thinks you have high to mid silver MMR and placed you against silvers when you had bronzees on your team. I know when you went from Gold 1 to Plat 5 or Plat 1 to Diamond 5 last year, usually your team had the lower MMR. So you would have a plat or two with yourself being Gold 1 and two other golds against all plats. That's how mine always worked in the past so I assume that's what happened with you in your placements. I haven't tried this year yet so Idk for sure. Just a guess based on past results.
As for the off topic conversation being had. So last season someone was Bronze 3 which is very low in rank. Riot added a new rank, which is lower than bronze, so it only makes sense for people in bronze 3-5 (probably some bronze 2's) to be in Iron this year. People who were silver 4 to bronze 2 are prolly bronze this year. People that were gold 5 to silver 3 are probably silver and so on. And yes, your first placement game is the absolute lowest rank you can possibly start. It only goes up from there. Doesn't mean you can't be ranked lower than where you ended last year. Just means that's the lowest you start this year. Hope this helps, good day everyone.