Yes, Wayland is a display protocol that applications need to speak in order to display on a Wayland server.
Applications built for X can still run on Wayland via Xwayland. But Xwayland is a bodge to allow legacy applications to continue running, an interim solution while toolkits, libraries, and applications are converted to use Wayland directly. To paraphrase the hit song:
Once we have enough Wayland software
At our call, hackers, at our call,
We'll throw out those dirty X code paths,
Ever more, hackers, ever more.
Applications built for X can still run on Wayland via Xwayland. But Xwayland is a bodge to allow legacy applications to continue running, an interim solution while toolkits, libraries, and applications are converted to use Wayland directly. To paraphrase the hit song: