hot temper and seriousness

There are a lot of things that it is difficult to figure out correctly. One of them is the defference between hot temper and seriousness. This might not be the right word for it. I often consider someone's action is serious or just hot temper. The latest example occured when I visit to my friend's house to Mito. Her son said to his mother, "Mommy, I want to eat a soft serve ice cream." Mamma said, "Let's have it when we go to the aquarium right after this." Her son nodded. Next, when we got to the aquarium, her son said again, "I want to eat a soft serve ice cream." But her mother said, "You should eat it after you enjoy the Dolphine show because the last show of the day will start right now." He got it. Then we went to the shop to have a long-awaited soft serve but the shop had already closed. Since then, he screamed for a soft serve and kept crying for a while. My friend tried to persuade him to give up a soft serve somehow but he won't hear her. I can't help admireing his persistence. Is this just hot temper or his serious action to express his claim to her mother? This example was the one regarding child, so you may say that it was just his hot temper. However, if this is the adult's case, he probably persuade someone to get something in gentler approach with patience. Maybe he tried it many times even though that annoys other person. In that case, which is the case?