Chests in ARAM preaseason?

Hey everyone!

Quick question - can you get chests in ARAM in the preseason?

I was just in a premade 3 for a game of ARAM and two of us got an S on a champion we hadn't earned the chest from yet :(

Cheers in advance for any help! :D

Note - there was no mention of the S's in the post game chat either, which was particularly weird...