MeshPatch creates a mesh. There is no tangency associated with a mesh - they’re just collections of facets. If you’re looking for a way to create a smooth surfaces through that set of curves - don’t bother, you can’t. Those curves are far too chaotic to be able to create a smooth surface, on top of that, the natural terrain curves have been cut with what are probably roads, walls and the like, creating vertical or near-vertical areas. Vertical walls wreak havoc with any Delaunay-based meshing algorithm.
You may be able to get somewhere with using MeshPatch on subsets of the curves as Pascal said, the whole thing in one go will not likely succeed - but I don’t think the results will be very nice. Maybe some other program might do better - not sure though, these types of terrain models are hard to do. In most cases I try to get the “natural” terrain without wall or building details, then adapt the terrain to the details.