well, posting the logic again.
to decide whether a function is even or odd, we check whether f(-x) = f(x) or -f(x) right.! hence if x ε {domain} implies -x (must also)ε {domain}.
and for ur second question.
i think the statement is regarding domain. inverse of an even function exists but domain will not be the same. for example f(x)=x2 → f-1(x) = ± √x . domain for f(x) is R while for f-1(x)=R+
let me know if i'm wrong for the second one !