No actually the ECS approach is more or less the exact opposite of (naive) OOP. In (naive) OOP you design objects for your domain, like an enemy, or a bullet, or an explosion. In ECS, you define abstract entities and compose data (and potentially behavior) on top of them, so there's no single "enemy" object, there's an entity that composes AI, geometry and sound effects to make it behave as an enemy.

In general, for large systems, this is a great way to achieve decoupling, where the naive OOP approach would get you stuck quickly.