It is not my algo, and I am also speaking on mesh welding. Rhinocommon uses an angle tolerance. Mesh edits weld and Petras weld use distance tolerance. That is point I was making 
The issue with angle is very often (depending how the mesh is made) mesh faces will have microscopic gaps larger than Rhino tolerance, even though it can join because meshes can join even when not touching as you know. The issue is if there is little gaps an angle calc between faces won’t work because it requires faces to truly share an edge, which they don’t on a microscopic level. By using distance you essentially average the verts of the gap to become one, within defined distance. The draw back with distance is if you have a very dense mesh you might weld verts that are very close to each other but didn’t want to weld, but I find it very less likely to have meaningful verts .001 units next to eachother so it is usually ok to weld by distance.
