Why did you reconnect? Who initiated contact? If you, what were you hoping to achieve? If her, why should she look up an old flame, if not in the hope of rekindling a romance? It just smells odd to me. Anyone who uses the word ‘platonic’ is already describing something that is a relationship, not just a casual friendship, in my experience.
Maybe your wife genuinely has no concerns. Maybe she does but doesn’t want to come across as controlling. Maybe she’s had enough of you and it’s one way to keep you out of her hair.