Often times spammers will send spam to random addresses at popular domains like hotmail, AOL, Gmail, Yahoo, etc, in the hopes that something gets through. Its entirely possible that they didn't get your address anywhere but purely by random chance. I've seen where someone created a new email, and just 20 minutes later spam was coming in.
As I said before, maybe I "recycled" the e-mail in another car-related website and forgot to make a note of it. Just FYI, that is a disposable address and on the notes to that address I noted that it was used on this site. I'll break it down for you:
"sunissxe-" that's the prefix, "subfor4" is the personalized tag, in this case it stands for Subaru Forester-related site #4, "@yahoo.ca" is self explanatory.