I have the following velocity measurements, where the sign of ${V}_{e}$ defines opposing directions of movement in a completely symmetric experimental setting:

$\begin{array}{|llr|}\hline {V}_{e}[cm/s]& {V}_{m}[cm/s]& \mathrm{\Delta}V[cm/s]\\ 9& 9.38& 0.38\\ 8& 8.491& 0.491\\ 7& 7.482& 0.482\\ 6& 6.502& 0.502\\ 5& 5.726& 0.726\\ 4& 4.499& 0.499\\ 3& 2.021& -0.979\\ 2& 2.34& 0.34\\ 1& 2.018& 1.018\\ 0& 0& 0\\ -1& -0.501& -0.499\\ -2& -2.328& 0.328\\ -3& -2.988& -0.012\\ -4& -3.503& -0.497\\ -5& -4.506& -0.494\\ -6& -5.762& -0.238\\ -7& -7.479& 0.479\\ -8& -7.981& -0.019\\ -9& -8.496& -0.504\\ \hline\end{array}$

In this table, $\mathrm{\Delta}V=\left|{V}_{m}\right|-\left|{V}_{e}\right|$

Running a Student t-test on $\mathrm{\Delta}V$, we find that the mean does not significantly differ from zero, under a type I error of 5%. From this result, I conclude that $\mathrm{\Delta}V$ is a random error.

The reviewer of my work (I'm an academic student) insists that my method does not account for the direction (i.e. the sign of $V$). That is indeed the case, since my test answers a precise question: Does the measurement method (${V}_{m}$) systematically over/underestimates the true velocity ($||{V}_{e}||$)?

Instead, the reviewer uses $\mathrm{\Delta}V={V}_{m}-{V}_{e}$ to show that the method significantly overestimates $Ve$, especially when ${V}_{e}<0$, using the same t-test. However, I am having trouble finding what specific question such a test answers, and the reviewer's statement is wrong in my opinion.

What is the correct way of defining $\mathrm{\Delta}V$ and discern a systematic measurement error?