The Apache software license allows anyone to take your project and release closed source versions of it.
There is no obligation for the forked project to share their closed source modifications back with you, the copyright holder. This is a feature of the Apache license.
The obvious next question is how do you prevent this from happening?
There is a well known solution. It is called the GPL. If he licensed his project as GPL, he would have the right to obtain the source code distributed by forked projects. He also would have achieved his goal of letting organizations keep private changes in house as long as they don't distribute their modified versions.
More open source developers need to know this and choose carefully.