.cs is just the extension that TorqueScript uses. As far as syntax goes, it's more or less similar to PHP, C#, C++ and that sort of language.
Functionality wise it's similar but there's a fair few differences. As far as "Torquescript is C#" goes, you can highlight TorqueScript using a C# Highlighter (that's what I do), but they're two seperate languages.
Not to mention that one's interpreted and one's compiled.