Have you seen a rank 3 ice minion? Different minions (that is, coming from different cards) tend to have different ranks.
The only way I've seen different minions coming from the same card have different ranks is if the card uses a varying number of pips. For example, Troll Minion uses 1-3 pips, and gives a rank 1-3 minion, depending on how many pips it used.
Balance Wizards have a summon spell that is called the Spectral Minion and this summons a random choice between an Ice Elemental, a Storm Elemental and a Fire Elemental. This may be the Ice Elemental minion you've seen.