The MO/overarching patterns are generalizations based on the core mechanics in each system. The expected behavior makes sense but in general, and most especially with Jung, raw behavior is not what determines type, it's cognition.
Introversion in Enneagram is a pattern of withdrawal. In Jungian typology it is a focus on subjective experience. Ne is an objective function but types who are dominant Ne can be withdrawing ("classically introverted") because it does not need people or even direct environmental experience to work. What makes it objective is its focus on patterns and possibilities that are not defined by the psyche itself; they are inherent to the world of objects. You can interact with those patterns without leaving the house, no problem. There is a reason ENPs are described as the "most introverted extroverts."
5s withdraw to learn and understand so they feel more competent and ultimately safe in the world. Is Ne-dom antithetical to that? It's not always hyper random crazy fun. It's certainly not as crazy as an ESFJ 5, where Fe is highly oriented towards other people.