Actually, if you read the quote you posted, it states:
(b) (1) A combination of vehicles which consists of a truck tractor, a semitrailer, and a semitrailer or trailer, may not exceed 75 feet, if neither the semitrailers nor the trailer in the combination of vehicles exceeds 28 feet 6 inches.
So, they are using the term "vehicle" to include a trailer for the purpose of "combination".
Basically, unless you have a commercial license with an endorsement, you are prohibited from double towing.