Sequelize's Knowledge

[Op.●] で where ● を表現してる。
Op.● が書かれてないと、デフォルトで = (Op.eq) が設定される。

Observe that no operator (from Op) was explicitly passed, so Sequelize assumed an equality comparison by default. The above code is equivalent to:

Post.findAll({
  where: {
    authorId: 2
  }
});
// SELECT * FROM post WHERE authorId = 2

https://sequelize.org/master/manual/model-querying-basics.html