Regardless of any person's credentials, you need to run claims through a common sense filter. The speaker you linked is 400mm high x 200mm wide and, while it's not stated on the page, could at the most have a 6-7" woofer. The graph claims <1% THD at 100hz and 110dB SPL. No test conditions are specified, not even distance. If the distance is shorter than 1m and/or a pair of speakers is being measured, and/or the speaker is in a corner, it might be a real measurement. But the fact that no test conditions are specified should make you very skeptical.
It seems very improbable that the claim could be true for 1 speaker, 110dB @ 1m. The KH420, the actual speaker in this thread, has a very good 10"(2-3x the driver area) woofer in a significantly larger box. At 98dB and 100hz it is already at 1% THD. So the referenced speaker is somehow playing 12dB louder than a KH420 while having lower distortion? Extraordinary claims require extraordinary evidence.