You are correct. As far as I can tell, they never launched as a trading card website. It's unclear if the code is related or not. There's a debate down thread about this and the only thing on it seems to be the wired article. So we don't really know what the code base started as (which is of course the real question, not what the site launched as).

Depending on how the trading card site was constructed, large chunks of the code base for exchanging cards could be used for exchanging Bitcoins (though not, obviously the broken wallet).

It seems like a question one should ask and one that should not be dismissed as merely "ignorant" or with the irrelevant assertion that the site is now owned by someone else when what matters is who built it in the first place and if that code is still in use.