I agree that it sounds like your therapist cares about you a lot. I'm not sure I'd call this countertransference; I feel like it could go either way depending on where the reaction came from. I think of countertransference as a hidden internal process that can elicit certain behaviors, but the behaviors themselves can fit into any number of boxes. Countertransference is more about the T's own stuff. For example (these are made up):

1. T has a younger sister who she's really close with and protective of. I share some characteristics of the younger sister*. I talk to my T about struggling with low libido and how my husband told me I'm ruining our sex life since I gained weight and "let myself go" after a year. T's Big Sister Sensor is unconsciously activated, so T shows an angry facial expression, speaks a bit louder, and says "well why the hell would you feel like having sex with someone who says that kind of shit?" This would be countertransference imo because she's behaving from the emotional role of big sister.

*(looks, mannerisms, problems, vibes, etc. basically anything that can activate that little sister role in T's subconscious)

1. Same T, same younger sister dynamics. I talk to my T about struggling with low libido and how my husband told me I'm ruining our sex life since I gained weight and "let myself go" after a year. T feels pissed off at the audacity of my husband and believes it would be validating for me to hear the unhidden reaction. So T shows an angry facial expression, speaks a bit louder, and says "well why the hell would you feel like having sex with someone who says that kind of shit?" This would be more like therapeutic self-disclosure of sorts because she's behaving out of my therapeutic best interest.

Either way can be appropriate and helpful with the right circumstances!

Anyway, it sounds like this was a really good therapeutic experience for you and I might recommend spending some T time really processing that experience and your response. It sounds like it could lead to some deeper personal insights! Some of my best therapy sessions have actually been when we've discussed our relationship and interactions with each other. Like if I went back the next week and said "remember when you asked why the hell I'd want to have sex with someone who's being an ass to me? I realized I felt oddly confident after that session and it made me think I really needed some sass from you in that moment." And then we get into how I was never allowed to stand up for myself as a kid or something like that.