This is a prime example of the difference in measurement between 5ers and trailers and how the truth is stretched a bit by mfgr's.
The actual measurement of a trailer is from end of hitch to rear bumper. Usually, you have to deduct at least 3 feet to get to useable space. Whereas a 5er is measured from the front cap to the rear bumper, and since there is no hitch protruding, no deduction.
I used to hate it when looking at trailers because they would include the hitch in the measurement of useable space, when in fact it is not.
I usually not how long they say it is, and deduct 3' and go from there.