Concentration of a solution of NaOH
Whatever that lye calculator is doing it is either wrong by design or internally correct and using a very obscure definition that no other chemist would understand.

Percentage solutions are always (barring calculators programmed by laymen) defined as weight of the solute divided by weight of the solution times 100. So a $\pu{30\%}$ solution of $\ce{NaOH}$ means $\pu{30g}\ \ce{NaOH}/\pu{100g}\ \text{solution}$.