Somewhat misleading headline. The IP trace led them to the couple but old fashioned techniques like surveillance provided the evidence to actually make an arrest.
It is interesting that having visited a website that's been mentioned in multiple mainstream publications seems to have served as grounds for surveillance. I hope there was more to it than that.
While it could be 'a visit' got them flagged I think it's more likely their selling weed on the site resulted in heavy usage which led to surveillance.