On partitions with $k$ corners not containing the staircase with one more corner

We give three proofs of the following result conjectured by Carriegos, De Castro-Garc\'{\i}a and Mu\~noz Casta\~neda in their work on enumeration of control systems: when $\binom{k+1}{2} \le n < \binom{k+2}{2}$, there are as many partitions of $n$ with $k$ corners as pairs of partitions $(\alpha, \beta)$ such that $\binom{k+1}{2} + |\alpha| + |\beta| = n$.