Not necessarily. It could be that way of course, but that’s not the only interpretation or possibility. I do know some people who never noticed the favouritism in their family because it’s “just the way it is”, and they were raised in a way that they mentally bought into the ‘reasons’ why the favoured sibling got more. It’s only once they were away from that dynamic and able to see how normal people interacted that they realised what was going on.
Now, I’m not saying that’s definitely the case here, I’m just saying it’s a possibility. I don’t see where there was any definitive sowing of discord in this relationship to be honest, but I can see how that might be occuring. Again, I think it could go either way, but wife still needs to back way off no matter which way it’s occuring in this situation.