It is really not close to this at all.
5E is one specific game. It is not a game engine, it does not even come close. 5E has fixed game mechanics, and they are pretty limited. If you even use the same theme (fantasy world with dangerous dungeons and monsters) etc. its even more limited
This is more akin to using a premade game from the unity asset store, then change some small things and release it. Which is called an "asset flip" when it comes to games:
Asset flip - Wikipedia
An actual game engine allows you to use any game mechanics you want, and does not define them for you, like an SRD which is a game mechanic document.
I can implement in Unity a game using any of these 188 game mechanics:
Browse Board Game Mechanics | BoardGameGeek when I use an SRD I use the exact same mechanics that game has (maybe I leave part away maybe I add some more).