CFI demeanor
For one thing, an instructor should not yell. I learned to fly in a 172 that did not have an intercom. My instructor did not have a naturally loud voice, so when he was trying to say something to me, he was shouting and it sounded like yelling. I don't liked to be yelled at, even if it is unintentional, and I probably reacted to him more than what he was saying. On the ground, he was just fine, just like your instructor. Just the same, I vowed never to yell at a student when I became a flight instructor. To the best of my recollection, I never did yell. I tried to be consistent in the airplane and away from it. It helped that my airplanes had intercoms.
Sarcasm? I can be very sarcastic. However, my initial approach when instructing and critiquing would be to just provide the facts in a dispassionate manner. Sometimes, after a student keeps making the same mistakes, I tried to say it differently. If that didn't work, sometimes I resorted to sarcasm to try to make the point clearly. Law of intensity.
I have to agree with 172driver about it being frustrating to give remedial instruction. You assume that someone with a Private certificate possesses certain minimum knowledge. Of course, we all know what "ass-u-me" means. It is disappointing to get a student who seemingly knows nothing and have to teach it again. That's why I preferred to have students who started in the program in which I was teaching, because I knew what knowledge they possessed. But, that doesn't mean that a new entrant cannot get up to speed and learn the program. It may mean that person has to do some extra studying.
Once again, I suspect that you have a good instructor. You were aware of his reputation for competency. Conscientious instructors strive to build that kind of reputation. Stay with it. As I said above, going from a learn-at-your-own-pace FBO situation to an intense and standardized 141 program can be major culture shock. I know. I earned my ratings with private instructors who owned their own airplanes and my first flying job was with ERAU, which was extremely structured. I had to summon up discipline and learn to believe in procedures that seemed anal and unnecessary because I was never taught them. I embraced them after I understood the rationale behind them and wished I had been taught that way when I was learning how to fly.
Once again, good luck with your training.