Go is much older than Swiss Tables. Since the hash table is a widely used container type and Go aspires to having a sort of "kitchen sink" stdlib I assume Go 1.0 had a hash table, and it can't be a Swiss Table because those weren't invented yet.

It's the "map" builtin. Go has a scripting-language-esque attitude of "you can build most things with arrays and hash tables". It doesn't completely preclude getting deeper but that's the general starting point.