Some accounts have subsections, meaning they are a compilation of a group of related metrics, ie. your sales account may include subsections like 'online sales' or 'store sales'. It's pretty easy to figure out that when you ask for sales, the number you get back is the sum of these two accounts.
The values located in an account for a group is not just the average of all the contributors. it averages all the values that aren't zero, so if a store doesn't do online sales, the average value of online sales doesn't get dragged down, giving you a better comparison. but, this means that when you have lots of stores that don't contribute to all the subsections of an account, the total provided at the bottom looks incorrect but is actually is the average for all stores that produce that value.
For the user, this means you should compare your sales value to the group's value and perhaps not compare it to a percentage a subsection makes up of the whole.