TFS originally had only TFVC. Now it has TFVC or Git for version control.
TFS is a big umbrella -- a suite of tools for ALM, including version control.
TFS/TFVC is just the original version control part. (1)
TFS/Git is just the recently added version control part.
The one thing that, alas, TFS does not do is bridge TFS/TFVC and TFS/Git. They are separate version control subsystems, and do not interoperate.
Some people have created various TFS and Git bridging utilities, but they have their own quirks and problems. From my coworkers who used them, the pain was not worth the gain. (2)
(1) TFVC was created by Brian Harry, the same person who created SourceSafe, and who inadvertently created what eventually became .NET because he hated COM. The origin tales of .NET are crazy wonderful, and show how innovation can come from anywhere.
(2) My coworkers were no slouches at TFS (the ALM), or TFVC, or at Git, or at another version control system called Source Depot only used internally. Because at that time, my coworkers were Microsoft coworkers, and we worked on a product called Visual Studio.
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