It seems to happen to me every few months, when I'm trying to highlight a web address I want to block.
It's such a dumb, bone-headed move. For instance, I'm using a laptop and the mouse pointer is screwy and it's a real pain to highlight things, and there I went accidentally clicking.
I think I've clicked accidentally three times, but never with this IP address, though I doubt that matters. I'm sure my IP is logged with my adsense.
Sigh. It makes me sick that I did that.