Did my site just get discovered by StumbleUpon?

I went from 0 to 70 referrals and is about to overtake as the place where most of my traffic comes from (I have others that are 70+ too).

Why is it all of a sudden appearing? My google organics is also going up 70+

It's not the best traffic either. They stay on average for 2 seconds. 88% bounce rate.

Its dragging my site's stats down.

Come up with a content locker to get them to stay on the site longer. They can't get on the site until they watch a 10-second video advertisement, for example. Now your traffic will stick around for 12 seconds