He’s right. Truth remains true no matter
whether anyone believes it. God found fault with the people. Let God be true though everyone were a liar. Etc., etc.
Truth also remains truth no matter who says
it. God has communicated truth through donkeys, little foreign slave girls, and even corrupt, pseudo-religious political animals like Caiaphas.
Everyone has an obligation before God to
identify truth and respond to it regardless of how that truth may be packaged.
The personal failings of the messenger do not excuse us from this obligation.