The nature of their site means that people will often display the following usage pattern:

-search Google for something like 'rapgenius track X'

-read the page covering the track that they're looking for

-close the page

Similar to songmeanings.net or other lyrics+ sites.

Or they are just looking for lyrics, and don't care about the interpretation. Then the usage is:

-search Google for something like 'track X lyrics'

-click the first link that looks correct

-close the page

As a RapGenius user, I use Google to search for specific links to pages since it saves me time from having to go first to the site then run a search. Also, it's not really a site that people browse, they go to look for a specific song so coming from a search engine would be the expected behavior.

Bear in mind that Google also effectively delisted them for searches like "<some song title> rap genius", and that since (like many sites) their own search engine apparently sucks, most people who knew about and liked the site probably got there that way.

I suspect that Rap Genius' bounce rate and user retention (both before and after this issue) is an order of magnitude better than all of their competitors.

what do you mean by 'retention'?

I imagine they mean that it is deliberately sought out as the source for people's rap lyric needs, but that it's sought out via Google queries (e.g. "birthday song rap genius") as the other comments suggest. Based on the response I'm seeing on Twitter it seems that many people believe that the site was inexplicably shut down due to its disappearance from the Google results.