Yeah the people who made it are in fact experts who have made the entire engine probably in C++. The industry standard.
As a hobbyist GameMaker wouldn't be a bad toy. If you want to seriously develop games you'll need to look into more professional languages. It doesn't necessarily have to be C++, it could be Java, Python, LUA, C, C++, C# or other languages that engines use such as UnityScript or UnrealScript.