On the Food network they boil potatoes, but they poach carrots. They poach turkey, but they boil eggs. They sauté' onions, but they fry eggs in the same pan. Likewise, they fry hash browns, but they sauté' onions in the same pan before adding the potatoes.
I can go on for days.
I think it’s a pretty accurate answer. The OP asked why it’s sometimes calked poaching and sometimes boiling. The answer being that they aare different things.