lol it is a quote from this popular comparison guide: http://www.head-fi.org/t/634201/battle-of-the-flagships-58-headphones-compared-update-audeze-lcd-2-revision-2-6-4-13#user_HE400
I imagine he means exactly what he says in this quote, but you can PM him if you want more clarification.
The HE-400's tonality is not "fun" in the sense that it is totally un-neutral - It is fun because it has a very specific upper-mid dip that allows the listener to home-in on specific instruments. The HE-400's tonal balance is not the definition of neutral, but it is also not the complete antithesis either. It manages to find a unique equilibrium between "colored" and "neutral."
Further on, he says this... which implies that the FR tuning improves how they sound but prevent them from having a true flat neutral FR curve. It sounds similar how I've heard that Sennheiser tuned the HD650 with a colored sound in order to sound more natural vs the HD600 which was tuned according to the FR curve.
MIDS: The mids here are interesting. The lower-mids are significantly forward while the upper-mids are significantly recessed. However, this is not as problematic as it sounds. The mids are recessed in the region where many odd nasal characteristics typically emanate. Here there is none of that. Of course, the recessed upper midrange will find detractors. It prevents this headphone from being "neutral." But I must counter this by suggesting that this coloration is not offensive to my ears, and I think many people may ultimately be won over by the headphone's ability to render detail without sounding shouty or nasal.
Now what the HE 400's lack of upper mids DO is make female voices sound wonky