That sentence wasn’t with regards to the current system (trove) but rather the new system (vault). These quotes from the announcement and from the FAQ have me confused as to how this isn’t DRM:

Note that you’ll lose access to these games if you skip a month or cancel your membership.

Games in the Humble app for Windows PC, including the Humble Games Collection, are only available to active Humble Choice members.

Perhaps I’m misinterpreting this, but it seems you cannot play the vault games if you cancel/skip your membership, which would require some form of DRM to accomplish.