Okay so I tested and found that this was not the case with either one of my meters.
ie, I placed both meters on an Arbitrary Waveform Generator and cycled through all of the waveforms and frequencies(up-to 100K) and found no indication of misreadings or deviations between any of the wave types down to the 3'rd decimal(3.915) in spite of adjusting /pushing wave symmetry, phase and cycle settings to the extremes.
And so with that being said, I'm going to call this particular claim a bust. Or at best, conclude that it is likely confined to equipment performance(china made meters) or perhaps older equipment. Though to be fair, my pen-type meters is fairly low-end and so I wouldn't get too carried away with such claims personally.