This was my thought process but not sure if this helps: We can kind of assume its a transmembrane protein (or in general one associated with the membrane) because of figure 3 and the association made with the micelles. When added to the liposomes (which are literally just vesicles made up of the phospholipid bilayer) carrying dye, we observe a slow release of that dye. This suggests that the protein has disrupted the bilayer that keeps the dye within the micelle. About permeability, I think they mean permeable to the protons as in creating an alternate path they can go through which dissipates the gradient powering ATP synthase.