Yes, it's normal for JPEG file sizes to vary quite a bit.
The file size reflects how much information there is in the image. In your image you have a lot of structure in the grass, concrete and leaves, which means that there is more information in the image.
Black and white photos will generally give larger file sizes, at least when saved as RGB rather than grayscale. Reducing unneeded color information is a big part of the JPEG compression, and in a black and white image there is no color information to reduce. The grayscale expressed as RGB means that the image has quite high contrast compared to a color image, so it has more information.