It IS only a 1.3 liter displacement engine.
BUT it used the 1.3L 3 times per revolution, instead of just once, is what he's getting at.
Imagine it this way.
A 2 stroke fires ever time the piston comes up to the top of the cylinder. This is like most SMALL lawn machines, and some motorcycles, mostly dirtbikes.
A 4 stroke fires every OTHER time the piston reaches the top of the cylinder. Cycles are Suck Squish Bang Blow. Down to suck in air, Up to make compression by "squishing the air, BANG to ignite the compressed air and MAKE power, blow, to blow out the used air and get ready to bring in more fresh Oxygen.
A Rotary has 4 stroke technology, but performs the process 3 times in each Ratation of the engine because the rotors have three tops to them. Each side of the Rotor acts as another piston, and the 13B's have 2 rotors, so BASICALLY, it's a HIGHLY efficient 1.3L O6.

(O6 because the rotors move in a circular, or figure 8 pattern)