A Dimensional Clarification and a Missing Moment Condition in Anomalous Diffusion Models with Sonin Kernels

This technical comment examines two points in Section 4 of Alkandari, Loutchko and Luchko, Anomalous Diffusion Models Involving Regularized General Fractional Derivatives with Sonin Kernels (Fractal and Fractional 9 (2025), 363; DOI: 10.3390/fractalfract9060363). For the equation on R^n, the total mean-squared displacement is 2n times the time integral of the associated Sonin kernel; the formula without n remains valid in one dimension or for a single coordinate. A Gaussian counterexample demonstrates that finite jump variance alone does not imply the leading quadratic Fourier expansion: centering is needed, together with isotropic covariance for an n-dimensional Laplacian limit. The note provides proofs, sufficient moment conditions and a Caputo half-order example. Includes the three-page manuscript, LaTeX source and reproducible SymPy checks. This independent preprint has not been peer reviewed.