The commas are just separators for the links, but what's most interesting is that you aren't seeing all the links. I found your ible with the same stats, but all the numbers in brackets seem to be missing for you, which is why you only see commas. I'm not sure why... maybe its a minor bug? or maybe your browser is preventing some elements from loading? But the numbers don't actually mean much in respect to a "referrer stat" because they are mainly from internal site links, like the contest you entered the project into. People who choose to open up your ible from that page are technically given a referrer stat, but because the link is instructables.com/..., its only represented by a number. I'm assuming its to prevent "instructables.com" by itself multiple times (when technically the link is different) and because posting the entire internal link would take up way too much room. The only slightly meaningful number, shown behind google.com (in my screenshot) is how many times people found your project through that route.