This is because of the low pressure at the mountains.
Step-by-step explanation:
The air pressure or atmospheric pressure is defined as the amount of pressure exerted by the air column of the atmosphere above in the atmosphere per unit area. This air pressure is inversely proportional to the height of the land above sea level. As we go up in the atmosphere, the pressure of Air decrease.
As Jackie goes in the mountains for his picnic, the pressure of air at the mountains is much lower than at her house in Austin, because Austin is at sea level. So water will boil much faster owing to low pressure. Thus, water is boiling at lower temperature. And this low temperature is easily and quickly achievable. So Austin seems that her soup is ready much faster. But the veggies and meat won't be fully cooked at that temperature. So although the soup seems to be ready, it isn't.