What I take from those statements is Brenda is trying to use mind games on the refs, trying to remind Don that if he fucks up there will be hell to pay and he'll be expected to make a grovelling apology.
Caixinha is essentially doing the same thing but he wants them on side, rather than scaring them with the potential fallout he saying these things happen, we're all human, no hard feelings.
If I was a referee reading those two articles I'd be naturally drawn to our side as we're less hostile towards them.
Caixinha knows what he's doing and just because their approach has worked for them in the past doesn't mean it will this time. I have to say so far that PC and his statement has really impressed me and not for the first time.