I don't believe that to be true as ideas can something come from integrating knowledge of different fields.
An anthropologist that learned a new paradigma about human reasoning from studying the way some African tribe reasons about the world can reasonable bring a new idea into computer science. He will need some knowledge about computer science but no 10k hours.
In http://meaningness.com/metablog/how-to-think David Chapman describes how he used AI problem by using various tools.
When takling one problem the problem wasn't that difficult if you had knowledge of a certain field of logic. He solved another problem through antropology. According to him advances are often a function of having access to a particular mental tool to which no one else who tackled the problem had access.
Putting in a lot of time means that you have access to a lot of tool and know of many problems. But if you put all your time into learning the same tools that people in the field already use, you probably don't have many mental tools that few people in a given field possess.
Paradigm changing inventions often come into fields through people who are insider/outsiders. They are enough of an insider to understand the problem but they bring expertise from another field. See "The Economy of Cities" by Jane Jacobs for more on that point.
I concede that a math expert can start usefully contributing to a math-heavy area fairly quickly. Having expertise in an unrelated area can also be useful, as a supplement, not as a substitution. I do not recall a single amateur having contributed to math or physics in the last century or so.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.