I guess he is alluding to effects of rounding up/down in small samples but those cannot be biased in one direction. Nor are they certain to happen.
If I toss 9 quarters and a nickel and count the fraction of tails that rolled on the nickel then it will be equal to 1/10 of all the tails only if all coins roll tails or all roll heads i.e. in 2 outcomes out of 1024. In half of the other cases nickel tails will be overrepresented and in in the other half - underrepresented. It's because you cannot roll a fraction of a tail.
If I toss 9 quarters and a nickel and count the fraction of tails that rolled on the nickel then it will be equal to 1/10 of all the tails only if all coins roll tails or all roll heads i.e. in 2 outcomes out of 1024. In half of the other cases nickel tails will be overrepresented and in in the other half - underrepresented. It's because you cannot roll a fraction of a tail.