Sandbox and traffic relation?

Well I was completely dropped from the index for a few days for one keyword. I had been building links... I read somewhere that perhaps the sandbox is a filter triggered by (amongst other things) a combination of traffic and amount of backlinks.
So I decided to buy some quality traffic from somewhere and an hour later I was back.

I guess it needs some more experimentation but just wanted to share this. Perhaps someone else noticed something similar?

Cheers.