I am not a lawyer, nor do I play one on TV. However, the license-back clause does seem to be written in relatively normal English language, and I think I may have some idea what this dispute hinges on. I:C have a license "...to sell products incorporating such Products to end users." Which, at first glance, appears to be precisely what they are doing with Whitefox and Nightfox now. However. . .
"Input Club (itself or with or through other entities) agrees to not distribute or sell such Products to resellers or distributors."
I suspect that MD view Kickstarter as the "reseller or distributor" muscling in on their turf here. But is Kickstarter actually reselling or distributing anything? I've been informed that sometimes they can, actually, provide such services to some projects, but I don't think that's typical, and I have no reason to think they're doing that for I:C. But Massdrop might argue that simply providing an online platform, or storefront, for I:C counts as being a "distributor", even though I:C would say they're the ones actually selling and shipping out their own keyboards.