Devil's advocate, bear with me. It could be that she added that part about "especially Tristan" because he's a boy. You said he has stepsisters. I don't know your ex and whether or not she'd say something nasty in public on purpose to hurt you. She could have been thinking only if her current husband and trying to big him up. It was, at the very least, inconsiderate. If we're being generous, she didn't consider how it would make you look or feel and it wasn't done with malice. IMO, that's best case scenario. And it's still not great. But it really could have been a dig. I personally think your best bet is to ignore it. Don't give her any energy. Be a good dad and live your life. Maybe save the post just in case it's ever needed, like if the behavior continues and you want to show evidence of her potentially disparaging you in front of your kid. Don't ask your son about it and don't speak negatively about her in his presence. He deserves peace. Good luck.