You're missing it. Here's what Joel is saying without saying it: C# 4 is "that language.". Both his companies are built on the MS stack.
Also at the time of this article they had their own custom language Wasabi. This article explaining Wasabi is dated a month after the original article:
http://www.joelonsoftware.com/items/2006/09/01b.html
It's based on VBScript, not C#.