If you have less than 25 ladder games played, chances are that you are still in provisional MMR :
- you have a displayed provisional MMR, which is generally lower than your true MMR, and from which your league is base (in your example, silver)
- And you have your real MMR, which is used to select the opponent you’re matched with (here around plat3).
So a freshly restarted ladder account could indeed display a silver league and match you with gold-plat opponents during that provisional state. Once that state finishes (≈ 25 games) the provisional MMR will go away, and only the real one will be use to place and match you.
It’s their MMR you should look at. If your silver 1 players have lost a lot recently, chances are their MMR is closer to your bronze 2 than their silver 1.
There are various elements that could affect an opponents’ performance : getting out of their comfort zone, changing style, further MMR (if you play when there are less people to be matched with), and smurfing. More explanations about those factors here.