An Apex Legends player posted a message from EA Help explaining why they were matched in a Platinum lobby despite being only Bronze. While the initial message seemed to clear things up calling it a bug in the system, it turns out to be a bit more complicated. A Respawn developer dug into the problem a bit deeper and actually explained that this was the system working.
It all has to do with premade lobbies.
As explained by the comment above. A Bronze player should never play with a Diamond or above player because of the intended spread, but Platinum could completely happen. The Bronze player was partied with a Gold party, meaning they will be placed in a Gold and Platinum lobby. When in premade lobbies, you're queued with the highest player. So it was completely intended for the Bronze player to be in the Platinum lobby.
This will tend to happen more in off-hours when there are fewer players available. Respawn doesn't want players to wait in long queues, so they blend the lines a bit.
Now if only Respawn could fix the current stale gun meta.