Well, actually it will. In fact, even correctly configured NAT won't stop connections into your network.
On top of that, it lulls you into a false sense of security, so you confidently think it's protecting you even when it isn't. At least not having NAT makes the actual state of your network clearer.
Port forwarding requires a port forward rule that matches the inbound connection. If there's no such rule... NAT won't stop the connection, it will just ignore it.
If no other aspect of your setup blocks the connection, it'll be successful. If you were deploying NAT because you thought it would function as a firewall then this part is probably not intentional.
On top of that, it lulls you into a false sense of security, so you confidently think it's protecting you even when it isn't. At least not having NAT makes the actual state of your network clearer.