Which was answered in plenty of different manners: different pings, packet loss, frame rate, data rate, bugs, it could be many of these things, alone or together.
The fact that 1 player is behaving a bit differently, while suspicious, does not warrant an immediate "cheater" label, because there are plenty of different technical factors at play that individualizes the observed behavior of each player.
For all you know this player could be playing using the default Modem configuration which could be severely limiting the amount of data he sends from his end, or be playing at much lower frame rate than everyone else (many no longer play at the standard 60fps, many either play at 120fps or 240fps or even higher, I play at 360fps for example).
It could even be a bug from NN itself which affects this player in particular for some reason.
There are so many possible reasons.
Again, you're the one who claimed to have 100% certainty this player is a cheater, so if you know something we don't know, just say it.
You're afraid of offending people if you do so?
That's a clear indication that you don't have any credible evidence whatsoever, because that doesn't many any sense at all.
In Apex Legends, a few weeks/months ago (don't remember how long) some players were spotted being able to dodge bullets like they were in the Matrix, by doing impossible animations and instantly crouching to the floor and then getting up as instantly and whatnot, they were next to impossible to hit.
Then, it was rather quickly found out that this was in fact a bug that only affected Crypto specifically, and it was a bug in the animations of this character in particular introduced with the update of back then.
This is a game in a much larger scale that UT99 ever was, so it was relatively quick and easy to understand the problem because it affected many players, however UT99 is currently in a such a state, that bugs of a similar kind may only happen to a specific few, which in a pool of maybe 100 players, there could be 1 or 2 with "weird" behaviors such as those.
And in those cases what you should do is investigate exactly what was going on, far before you even consider publicly accusing the player of cheating, because you never know what you may actually find out.
You talk about "truth": truth is reliance in proper investigation to find out the actual facts, not hearsay from people you may consider an authority on this subject, because there's no such authority to begin with.