Before arriving at a conclusion, the context must first be established, that is, why the teacher apparently said that. Passing judgement without knowing the prevailing circumstances is at most subjective.
Frankly, I find excuses such as "teachers should be mature" and "students are still growing and learning" quite lame. Why?
Firstly, nobody is perfect and even the most mature adults have feelings and make mistakes. So everybody, young or old continue to grow and learn the lessons of life until they die. Age is not an indication of maturity level.
Secondly, if we seriously want to learn and be more mature, we have to learn from our (and others') mistakes. If the only thing we do is to point a finger at others, we will fail to recognize our own mistakes and be accountable for our actions. When we fail to be responsible for our actions, how can we learn and grow?
Thirdly, it is pointless to argue over who is right or wrong, because people will end up denying their faults and accusing others. It's happening right here. Isn't it more fruitful to ask, "What can I learn from this episode?"?
Lastly, whether you like it or not, there will always be conflicts between teachers and students. Difficulties encountered in the sheltered school environment, compared to challenges in the adult world are, I would say, peanuts. So, it'll be wiser to learn how to shoulder responsibility, handle conflicts and solve problems positively before leaving school for the real test of life.