I expect you can guess the difference between grayscale and black and white based on the names - essentially black and white contains only those two, while grayscale has assorted gray shades as well. Black and white can look casually grayscale at high definition where the blacks and whites are mixed (a 100x100 square with 50% black and 50% white equally distributed throughout is going to look gray on first glance at a distance).

I can't say if your image is grayscale because I have not properly looked at it - it just feels that way on first glance. I'm also not familiar with digikam so I don't know what it defaults to when converting color to monochrome.

I do like the composition, btw.