Google + increase in traffic = boost in SERPs?

I've noticed something odd recently and I was hoping that someone could help shed a little lite on the subject of traffic and SERPs. I keep reading that an increase in traffic will not help your rankings in the SERPs (ie buying traffic). However, recently I purchased a directory submission for one of my sites and there was an increase in traffic on the day of submission that was about 10 fold above average. The following day, traffic began to return to its normal volume. I didn't think much about it until about two days later when I jumped from mid page of page two to mid page of page one in the Google results. I keep a close eye on all my links and nothing changed prior to or subsequent to my jump. The only change for my websites was a large jump in unique visitors on the day of the directory submission. Of course eventually my website returned to mid page of page two but it dropped slowly over a course of three to four days. Have I missed something?

It's possibly the backlink from the site.

That was one of my first thoughts but I dropped back down to my original position (before the directory submission). I would think that if one of the links gave me a boost I would have stayed on first page.

I also experienced this Awayler. I don't have tons of backlinks and if I have I'm sure they are low quality. My focus is using twitter for my client to gain traffic and yet I noticed that the SERP ranking of his site is dramatically increased. Maybe this is they called "the best 2010 Google ranking method"