The terms “high” and “low” originated from the type of practitioner rather than the type of magick.
In ancient times, things like candle magick, rootwork, etc, were practiced by the slaves, servants, farmers and the uneducated, the people mostly concerned with just getting through the day. Magick for the harvest, weather predictions, rain making, the use of plants for healing, the use of animal parts for amulets and talismans, balms, and salves, were the domain of the lower caste, hence the term “low magick.”
High magick, on the other hand, was originally the domain of the educated nobility. It required the ability to read and write, knowledge of mathematics, chemistry, physics and languages such as Latin and Arabic. Operations utilized precise astronomical calculations based on planetary positioning and often used complex diagrams (look at John Dee’s Enochian journals as a good example). Such operations could take several hours or days to perform, but of course the upper classes had all the necessary leisure since they didn’t have to work for a living.
In modern times, the majority of people are now much more educated than those of ancient nobility so the terms high and low are less used but when they are, they are generally used to refer to certain magical practices instead of the practitioner and have taken on a somewhat moral or ethical perspective, high magick, being mainly theurgy and focused on improving the self and becoming like unto God, and low magick being thaumaturgy, and more concerned with material needs. However, the truth is there is quite an overlap as the high magical operations of theurgy could be used for material ends (and often are) and the low magick operations could also be used to become closer to God (or gods).
As for pathworking, the name comes from the Kabbalistic practice of walking the 22 Paths of the Tree of Life. It did not originally directly involve spirits, but only certain correspondences and imagery specific to the Sephiroth one was seeking. However, it has now becoming a catch-all term used to generally refer to any imaginative sensory imagery used for spiritual contact.
I’m not sure who started using the term pathworking for such operations, but I think it may have come about because such workings generally involve a select group of spirits and a specific purpose or goal for the magician, and hence can be considered a “path.”