Because T series can back fold the tripod, meaning the Ball head will be inbetween the legs when folded. So the shorter length you saw is 34cm. (meaning just legs will be visible) You will need to reverse fold the legs to start using, good for packing up and go, but quite troublesome when you are shooting on tripod AND moving.
For the 40cm one is when the ball head is exposed. This one allows you to setup the tripod faster as you do not have to reverse fold the tripod to use.
I got a T1004X does the same thing as well (just longer). Hope this helps