I could be wrong but I think only 14 activity points are given within 2 weeks. (Double check). You will need about 30 to become a Junior. So unless he has a hack or a friend on the inside, I don't see how he pulled that off.
Yes, this is what I was about to say. But I remember stumbling into one guys' account and he joined the forum less than 2 weeks ago and he is already a Junior level!
I didn't know the guy so obviously I couldn't ask him how he did it.