A bitmap was also known (in ye olden days) as a raster (the term is still in use in some circumstances)
When there used to be just monochrome monitors, bitmaps did indeed have bits in them!
When colours were introduced, the term pixelmap was introduced for coloured images.
Nowadays, “bitmap” can refer to 2D arrays of bits or colours.
Logically, bitmaps are 2D arrays, although in fact they may be stored by other means
– Java 2 uses a 1D int array