  More and more halo nuclei or candidates have been identified or suggested in
experiments in recent years. It was declared that the halo structure of
$^{22}$Al is revealed by the large isospin asymmetry in $^{22}$Si/$^{22}$O
mirror Gamow-Teller transitions [Phys. Rev. Lett. 125, 192503 (2020)]. We
highlight that a significant mirror asymmetry already exists between wave
functions of the likely unbound nucleus $^{22}$Si and the doubly-magic nucleus
$^{22}$O, which largely explains the observed asymmetry in the transitions.
Furthermore, these transitions involve only the $1^+$ excited states of the
daughter nuclei $^{22}$Al and $^{22}$F. The $1^+$ state of $^{22}$Al cannot be
considered a halo state due to its proton-unbound nature. An analysis of the
spin-parity suggests that a weakly bound $2s_{1/2}$ valence proton in the
ground state of $^{22}$Al is improbable. To investigate the shell structure for
the ground state of $^{22}$Al, we employ the state-of-the-art deformed and
triaxial relativistic Hartree-Bogoliubov theories in continuum. We find that a
small $s$-wave component of $5\%$ appears for the weakly bound valence proton
in $^{22}$Al only when triaxial deformation is considered. While the
examination of densities and rms radii indicates that this small $s$-wave
component is insufficient to form a discernible proton halo in $^{22}$Al,
slightly larger $2s_{1/2}$ occupations have been reported in other recent
theoretical results. The question of how many low-$\ell$ components are
sufficient to form a proton halo in the presence of the Coulomb barrier remains
open. Thus, future measurements of reaction or interaction cross sections and
momentum distributions of breakup fragments are highly desirable to verify
whether $^{22}$Al is a halo nucleus.
