From my perspective, this passage is spot-on. I have experienced very similar things with my T. One time she made a very minor and understandable mistake (think logistical thing), and I got intensely angry. She got me in for a sooner appointment (same day), and by the time I got there I felt guilty for being angry because I knew it was just an honest mistake. She was able to draw out the hurt and deal with it in an understanding way, even though I could tell that she herself was feeling very sorry about having made the error. It would have been easier for her to apologize profusely and shut down the irrational anger (we both would have felt relieved then), but she knew that it would be helpful for me to have somebody really hear and understand my anger for once in my life. She was tough enough to really listen and explore it, without getting defensive about her mistake. And it was a huge moment in my therapy. I'm glad she handled it gently and made it into a growth opportunity for me, and I know that it strengthened our relationship. (She did apologize at the time and has even mentioned since then that she regrets the mistake, even though I am super over it.)

Reading your post, it kind of sounds like this passage made you question whether you want to leave your current T, and if so, I'm wondering why. I understand how rare it is for you to get attached to somebody, but this T does not sound like somebody who is secure or experienced enough to do this for you. Think about the interaction the passage describes: Calm, safe environment, you're freaking out, the therapist is emphatically NOT freaking out. The situation stays that way for as long as you need it to for you to become calm and to feel understood. The T understands (even without you having to recognize it) that the intense stuff is about you, not about her. You can be extremely upset with the T about something that is not even her fault (sick kid) and she STILL isn't getting defensive or upset. Does that sound like something you can consistently expect from your current T?

One thing that maybe isn't clear about finding the right person to have this experience with is that they are actually (counterintuitively) unlikely to activate a strong attachment response from you right away. And by right away, I mean it might take months. Healthy, stable people seem unbelievably boring when you are used to chaos being necessary for you to get that intense, connected feeling. I'm super attached to my T, but it took years for me to get to the point where I felt that way about her and thus could do this kind of work. It sounds like you are ready now, so it might happen faster for you if you are willing to be brave, but I personally am 100% sure it needs to be with a different T.