Almost correct. You may consider it as a split GPL license. Because the mentioned above header code is located in
open source PHP file which can be distributed as GPL.
As far as you know, the
split GPL license allows to have open source GPL file along with proprietary ones. E.g.
RedHat Linux which package has both GPL and non-GPL files. The GPL file can be re-distributed, the proprietary ones - can not be since they are covered by another license.