when you download from within the Kindle app, it puts the files in the folder specified by loocid and the Kindle app will often rename them some godawful random alpha-numeric and split the file into constituents like cover, text, etc.
from what I understand, GoogleBooks does the equivalant, hoping to bust your chops into only using their books, ecosystem, etc by making things difficult....
when you download with a file manager or via usb, you have control and put them where you like with the original name.