Certainly you're right about the department store thing being credit building, but more importantly, they will usually sell your info to the big banks as well, so you get on their mailing list at the same time.

Your method probably ended up being faster given your situation, I was just pointing out that for US citizens, your name usually starts getting passed around by the time you're 14 or 15, so by the time you hit 18 or 19, they're already slavering to collect those high-interest payments while you still don't have an extensive credit history. :)