Yes, this is true. Indeed, it is not advised that you put hot food in the refrigerator so that to prevent condensation and heat increase inside the refrigerator. As such, a hot food should be kept outside so that it is cooled before being put in the fridge. This would typically last for a maximum of 2 hours (1.5 hour in hot weather).
On the other hand, we should also note that some foods do not need to be refrigerated. They may even lose their value if placed in the refrigerator, such as exotic fruits. Also, fruits and vegetables that need to ripen (such as tomatoes) must remain at ambient temperature.