The word "professional" may or may not be the best word to be used here, because in English the antonym of "professional" is words like "tyro" or "amateur." Which is misleading, in this case.
When a corporation deploys hundreds or thousands of copies of a system, they rely upon the vendor of that system to provide not only "the system itself," but troubleshooting and even custom configuration. Various vendors, such as Red Hat (and IBM...) have zeroed-in on that requirement very specifically.
Every distro is working from the same basic code-base, and Linux is a professional-strength operating system in every way. The phrase "professional version," therefore, isn't to be construed as being indicative of the software itself.