Because one of the main authors behind JSR-310 happens to be the JodaTime author and considers it to be inspired by JodaTime, even if it's different to fix some flawed assumptions JodaTime made [1]. And as far as practical use goes, they're very similar, since they draw upon the same concepts. I don't see how it isn't a fair description, especially when you compare to how bad Date/Calendar are right now.
[1] http://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941....