Note: While this concept looks similar to the object property feature, there is an important difference. For normal object properties the property value is of the same type as the defining getter method. A relation method however returns an yii\db\ActiveQuery instance, while accessing a relation property will either return a yii\db\ActiveRecord instance or an array of these.
Yii2 docs
У меня хоть и не связи, но логика та же применяется.