Went to test if stopwatch showed velocity during down hoiks and it does. I guess it makes some sense, because there were signs that game considered your character to be falling during downhoiks. What makes less sense to me is that holding portal gun seems to make you hoik down faster. I used hellevator hoik from Hoik_Demo_World0_2.wld and just by eyeballing the time it seemed like without portal gun it takes 4 seconds to go down, and with it takes only 2. I'm guessing you're clipping past some of the hoik teeth when you're falling too fast, and that falling stars autohoiking themselves is part of the same effect(they don't seem to be falling all that fast though, so effect might be observable without portal gun too). Might be an interesting quirk, but I can't think of a use for it, so I probably won't explore it any further.