Referrer Spam

Referrer spam shows just how ingenious black-hatters can be in finding ways to manipulate search engine rankings. When someone clicks on a hyperlink their browser opens up the new web page. As part of the communications process (called HTTP which stands for HyperText Transfer Protocol) their browser sends the web address (URL) of the page containing the hyperlink. This address is called the Referrer. The user's web server will log this address and it is useful for traffic analysis, for example to judge the effectiveness of inbound-links.

Referral spamming is related to referral logging on the webserver logs, intended to collect information on who visited a website and how they happened to arrive there. Spammers make use of this.
When you click a hyperlink on your web site, your browser passes to the next site the address of the page where you clicked the link. This is logged by the server hosting the next web site. Using scripts these types of logging could be done in a repeated fashion resulting in large number of referrals in the victim domains log. Many search engines uses the number of counts of these http referrals to determine hits and popularity of websites.

Also from the reply to the post you have mentioned, it seems that the tech is talking about rewrite rules by which the http referral logs can be rewritten accorinding to ones desire. Thus the number of referrals in ones log can be increased. But for this the logs should be accessible to the public. But here the logs of the domain is in the path /usr/local/apache/domlogs/domain.com.

modsecurity rules in .htaccess file under public_html folder

#Mod security rule to block referal spam.
SecFilterEngine On
SecFilterDefaultAction "deny,status:412"
SecFilterSelective "HTTP_REFERER" "(holdem|poker|loan|mortgage|hold-em)"
SecFilterSelective "HTTP_REFERER" "fromwhichdomainname"