Stability and Positive/Negative feedback
You are not reading the words carefully. Tomato sauce is used to make a pizza, but not everything made with tomato sauce is a pizza.

Yes, positive feedback is used to cause oscillation. But that statement does not say that a circuit with positive feedback will always oscillate.

Similarly, negative feedback is used to achieve linear stable operation. But, the statement does not say that a circuit with negative feedback will always be stable and linear.