The way of Black Hat to increase their traffic. Some people is called with spamming link building. (after google update to hummingbird this way will killing them because irrelevant link building). They're just unknown about of it.
I used to get those a lot. Porn and pill peddlers. They would try to spam my blogs and forums with cheap pills and porno. I let them build up in a redundant forum then purged and blocked it and redirecting back to my main index page.
ASR would pick up the movement and boost my ratings. Not sure how that works but it did.
Maybe they just want to end up on your list of backlinks. Webmasters get curious when they see they get traffic from a site that they don't know and is likely to visit the site to check it out, which is exactly what they want. They don't need to have a link to your website anywhere. All they need is to send the Referer HTTP header.