They're obviously just burning one of the crappier, less significant names for an OS release that's all about bug fixes. Where's the real surprise and shock in that? Just like Snow Leopard aimed to improve on the performance of Leopard, El Capitan refers to a landmark within Yosemite to designate that it's not a major feature release but rather a bug fix release. It's a derivative of the prior release's name.
I am still looking forward to when Apple introduces an OS X "Golden Gate," but I feel they are likely holding onto that for a very significant update.
At the end of the day, if you so choose, you can just call it OS X or OS 10.11. Nobody forces you to use the moniker Apple tags to their operating systems. Personally, I've always felt weird using these names in verbal discussions. Saying you're running "Tiger," "Leopard," etc. is likely to confuse somebody not acquainted with Macs. When Android people tell me they are running "Jellybean" or "Kitkat," I have no idea what the hell they are talking about.
Although, when somebody says they are running "Windows 8," everybody immediately knows what is meant. And then, this is generally followed up with awkward silence, condolences, and sympathy.