快５岁child sometimes does not really know what is worng or right

My son is 6 and half now. When he was around 5, he sometiem said things that were not facts. But he insisted what he said were true. I talked with his teacher. She told me that at that age, kids sometimes does not really know different between facts and believe/imagemation. Try to avoid telling him "you are wrong" directly. Try this: Mom does not understand why, can you explain to me?