This is not the anecdote I'm familiar with. My understanding was that Will (or someone else) noticed that people were having a little too much fun farting around in a content creation tool they had written in-house and they decided to make it into a game of its own.
Your inspiration for the love song you just wrote is the special someone you have your eye on. The lyrics are informed by every other case of New Relationship Energy you have ever had, with bits borrowed from friends, books, and movies.
Was Will really studying urban planning for giggles, put 2 and 2 together and got 5? Or was he working on a hunch about a city planning game and what he found cemented his hunch?