Isn't that how we normally measure rated power? And the current limited note - that just means with a 2ohm load it runs out of current before volts - that is hardly unusual - Id suggest it applies to almost all amps - if they can't double power from 4 to 2 ohm, then they are current limited.
And the measurements here of the Ncore amps show the noise/distortion by frequency, also showing the point at which clipping starts. (Chart from the NC252)
I find it far more likely that the speakers are distorting than the amp is.