Rivers on Earth are cut by water into hard rock. On Titan there, they may have been cut by liquid Ethane into solid Propane (or something like that). The difference in density, and more importantly, in viscosity, between the "fluid" and "solid" was likely much, much less than on Earth. Maybe more like hot syrup cutting through jello. I also think there is some analogy to the dendrites seen in moss agate, as well as dendritic river patterns. Perhaps these are partially eroded dendritic inclusions, and as such, do not have to connect, or make sense as a distribution network. I have seen subtle patterns like this in dissipating clouds - even though there may be a net and continuous flow, the strings of meandering particles or condensate often do not connect, but only occupy zones of higher pressure or shear. I would call these "cloud dendrites." Maybe these river features are such eroded condensate filaments, or a former river system now eroded beyond its former base level.