no, it wasn't - mostly because of political bullcrap coming from the "I'm purer than thou" crowd. obviously, the biased perception that gnome was using C# exclusively was also due to the same crowd.
this also led to the C#/mono platform lagging behind, so that these days writing gnome apps in C# means using deprecated libraries, which is unfortunate.
Ah right, maybe that's where I got the impression. I used to follow Nat Friedman and Miguel de Icaza's work in the early/mid 2000s and picked up a 'C# is the future of GNOME' vibe.
this also led to the C#/mono platform lagging behind, so that these days writing gnome apps in C# means using deprecated libraries, which is unfortunate.