It's hard to tell what the Kobo Glo progress bar is actually trying to say: whether it represents progression through the chapter, or through the whole book. Does the progress bar represent progress through the book, or through a the current chapter?
It depends on the format of the ebook that you are currently reading (Kobo readers have different reading engines for different file formats).
When you are reading standard epub books, PDF's or comic book formats (i.e. CBZ), the number shown represent the total progress of the book.
When you are reading kepub files (it is basically a standard epub with a different extension and some optimizations made by Kobo), the default behaviour is to show the progress of the current chapter, not of the total book.
However, this can be changed in the settings of the ereader, so in the end you can make it behave like you want.