See they talking about linearity only not regularity.Most of us can confuse in it.
But Chomsky hierarchy says that=>
every CFG is not a linear G( the grammar which has at most one non terminal in RHS) ,but every linear G is a CFG.
we also says that CFG is a superset of linear G.
and moreover, linear grammar is a superset of RG.
linear grammar have special two version:
1)right linear G
2)left linear G
which are RG.
so the given grammar is linear.
i hope its helpful.