I didn't know openjdk was developed by Oracle. I always thought it was a community implementation of java as opposed to Oracle's proprietary implementation.
Sun's JDK implementation was made open source (GPLv2) in 2006 and dubbed OpenJDK.
Yeah its like George Lucas, doesn't matter you care for the Jedis or the Dark Side or even Jar Jar, he owns them all.
It was Sun's project before Oracle bought Sun. Sun worked a lot with Netscape back in the day to make Open Source Software happen at all. From 1998-2004ish, Netscape and Sun were the open source projects and the strongest proponents of the licensing and development models. Oracle absorbed all that good will with the purchase.
It is a community implementation although the vast majority of contributions come from Oracle staff. RedHat, in particular, has made numerous contributions.