Dimensions of a spectral representation
It does have two dimensions. An image of size $N \times M$ has two dimensions. Three dimensions would be $N \times M \times L$, and so on. For each pixel with coordinates $x$ and $y$, in two dimensions, you have a spectrum magnitude value.

However, if you start treating rows or columns of your spectrogram as vectors, then you're interpreting them as 451 points in 128-dimensional space or 128 points in 451-dimensional space. This is different.