  In a recent paper by N. Santowsky et al. [Phys. Rev. D 102, 056014 (2020)],
covariant coupled equations were derived to describe a tetraquark in terms of a
mix of four-quark states $2q 2\bar{q}$ and two-quark states $q\bar{q}$. These
equations were expressed in terms of vertices describing the disintegration of
a tetraquark into identical two-meson states, into a diquark-antidiquark pair,
and into a quark-antiquark pair. We show that these equations are inconsistent
as they imply a $q\bar{q}$ Bethe-Salpeter kernel that is $q\bar{q}$-reducible.
