I think this statement is just a little too strong. I've personally played plenty of games where I baited the opponent into scratching on the 8 or making the 8 early. That's not a fluke on my part - it does take some skill to recognize the situation and set your opponent up. However, I do agree that most of the time it isn't a reflection of my ability at all, and for that reason we make adjustments.
By the way, a system where those "flukes" aren't even recorded (say a system that only looks at games won or lost) is also susceptible to this issue. If you believe they shouldn't count at all then they shouldn't count there either. If you believe it all evens out in the long run then you should believe that here as well.
Also, if a player is going to sandbag by losing games, how they lose is irrelevant. A cheater will do whatever they have to do to cheat. You can make it harder, but in the end you're not going to prevent it 100%. You have to be vigilant and try to catch what you don't prevent. If someone tells you their system can't be sandbagged, they are naive and probably not vigilant at all.