Well, he's probably not a sound tech, but still he got the physics right, it perfectly make sense:
2 x 8ohm speakers per channel gives you a total impedance of 4ohm:
And if you look at Amp label:
LOW
A or B: 4ohm Min /SPEAKER
A + B: 8ohm Min /SPEAKER
It just confirms that calculation, either one 4 ohm speaker per channel
OR
two 8 ohm speakers per channel.
I don't know about you guys, but I believe in science and not religion.