PH automating followers? Please enlighten me...

For the past little while I've been getting follower notifications from PH, and I have no idea why. I don't often visit the site, and I have very little activity there. I went to check out my profile, and was shocked to see that I'm following hundreds of people, and have no recollection of when I did that.

Am I having a huge memory gap, or is PH just making people follow each other in an automated way?