The argument is that choosing between two alternatives only requires a person to rank them in order of value. The chosen option is preferred to the option not chosen.
To choose between two alternatives does not require a person to assign cardinal numbers to the amount of utility received from each alternative. Option A generates 10 units of utility and option B only 6 units of utility. Most economists (not just Block, Rothbard, and others Austrians) reject cardinal utility as such.
In 1954, Gerard Debreu, a famous French economist, showed that it is possible to represent an ordinal rank with a cardinal utility function under certain assumptions. In this conception, one cannot say that a tie is 1/4 as valuable as a pen (even if the tie has 4 utils of utility and the pen has 16 utils) because the different cardinal numbers only represent ordinal ranks.