I don't think this is it. I can only find one tweet from an Apple employee who said that they can't work on OSS and was looking for new maintainers. I am not sold that this is the whole truth.
I think the bigger issue is contributing to OSS for putting Linux on a Macbook for example could be considered leaking company secrets since you would have access to internals. I find it hard to believe that Apple would go after someone for making a open source calculator app.