There are a few other potential factors:
For one thing saying someone is in Bronze II is really very vague sort of way of saying what skill level a player is at. The League system is somewhat loosely correlated with a players hidden ELO. So you can't actually use the fact that they were ranked Bronze II to precisely predict where they will end up.
A second potential factor is that accounts playing ranked for the first time don't have the decayed hidden ELO of accounts that ended last season in the general vicinity of Bronze (in terms of their hidden ELO). This means that new accounts can often place higher (say Silver) than their Bronze counterparts of equal skill level.
Neither of these factors is a bug, but it can upset players that don't understand how the system actually works.