You're thinking like an engineer, not like a lawyer. Does HumbleBundle expect you to use the official distribution channel, which is a torrent? Clearly, yes,

You're thinking like an engineer, not like a lawyer. Does HumbleBundle expect you to use the official distribution channel, which is a torrent? Clearly, yes, so using the official distribution channel (and all subparts of that operation) must be OK with them. (This is called "implicit license." It doesn't have to be explicitly spelled out in the ToS, just like most non-pedantic lawyers won't bother to write "We grant you a limited, non-exclusive, non-transferable license to make one (1) copy of our webpage within your computer system for the purpose of 'caching.'") Rightsholders can arrange for many, many things which are illegal for non-rightsholders to unilaterally decide to do. That puts the "rights" in "rightsholder."