Looks like it's a Reading level test.

1) Kids can have off-days. They can feel sick, or tired, or angry with the teacher, etc.

2) Just because a child's IQ is high, doesn't automatically mean their achievement testing will also be high.

Here's the website I found - http://www.riversidepublishing.com/products/gmrt/index.html

It looks like it's a very long test. Is it possible your child got tired and didn't finish? An hour is a long time to test a 7yr old, IMO.

~amy