It's a bit of both really.
There probably is an update, and somewhere in Google it might be referred to as Zebra. However, since Panda kicked off a lot of SEO sites found that their page views were going through the roof. As a result, any time they believed a major update was coming (or not) they decided to give it a name and to scare everyone.
Google updates its algorithm constantly, and they test different variations of it in different areas at different times. They don't just sit back, come up with a name and release it like some "product".