I think this is hard for extroverts to understand. They think that if being with people is draining, then we must not like people. On the contrary, we want and like our friends as much as anyone, we just need that quiet time to fill up again.
It states that ISTPs are stubborn. I personally prefer the term resolute. I agree that we are generally easy going. And, really, I do not see that the two are contradictory, much less mutually exclusive.