> You do not have to be a lightning node operator before you can open a channel. You do not have to be a node operator also before you can use lightning network for making transaction

Yes, this is true, you can use LN without opening channels, by using someone's else channel. But if you are not running your own node you don't have control over the funds and you are relying on a thirdy party. It is the equivalent of letting funds on a exchange. The saying "not your keys not your coins" is for bitcoin layer 1, while for layer 2 it would be "not your [LN] node, not your coins"