These are not the same things. The major difference is that hardware for instructions can do only one thing so it can be thought of more like a physical proces

These are not the same things. The major difference is that hardware for instructions can do only one thing so it can be thought of more like a physical process. For a software pipeline, you don't need to hand data off to a different thread, you just need to make sure the data is run with the right execution. That could be on any thread, and the execution/function can be run on any number of threads at the same time as long as the data is separate.