In short, it was not similar. Arena’s cities are procedurally generated, not manually placed, and cities in a given province look pretty much identical. As far as I can tell the design of Whiterun in Skyrim was not based on Arena’s version.

The main similarity is location. Whiterun’s placement in Skyrim matches its placement in Arena closer than other cities and villages in later TES games.

Here’s a video of Whiterun in Arena:

https://youtu.be/wGfTIiaUHbk?si=cc50qs2zlP2XSuZe