I've spent 11 seasons playing heavy(sandbagging for life), and WAY TOO much time doing heavy v heavy ammomod mge to tighten up those last few %s of tracking, I like to think I'm rather good at by it now, at least in some parts of the heavy class. What keyed me off though wasn't just his tracking, which went from eh, to fucking on point, but was the mid range and longer damage number and their ticks, which looked higher and more frequent than they should of.
Remember Heavy fires in a random spread cone, and even with prefect tracking you'll miss shots because of that spread, its possible he is the luckiest heavy in the world with where they were landing, which was always on target, but I suspect a bit of spread reduction.
As an aside I use 2.5ish per 360 as well, and often I look smooth from POV when tracking, and can do stupid fast flicks, but its the changing off target that looks suspicious as well, with that high of sens there is almost always a "wobble" when you change direction or flick to targets, it just happens from the movement of the wrist when .31 of an inch moves your aim a whole 45 fucking degrees, aka half way across the screen, with such high sense (other heavies here can back me) there is almost always that wobble when pulling and a target that started to move diagonal or that fraction of a moment where you over-aim on a juking target before you drawback. I've practiced and cut mine down to pretty close (within ~5%) as a I think a person can with a heavy aim, obviously bots are going to beat people hands down every time though.
When the suspected moments occurred you never pulled off even a juking moving target or missed a shot, not even for a moment. Or hey maybe you are just that good or lucky, which would be nice because you are a chill guy, but I mean come on...