Not GP but I'll often do so to test the heat. Doesn't read like that's what they meant though. It'd surprise me to learn that it made a difference either way to flavour or anything.
One is seasoning aromatics, the second is making a more even veg coating than seasoning at the end does; stirfry vegetables at a high heat won't release water thus won't have a 'sauce' to carry seasoning across the surface, this method makes it more even.