Can you get Kicked out of Preschool????

My son Monkey boy is having a real hard time in Preschool this year. Therefor I'm having a real hard time too. At Preschool pick up last Friday he was not in the classroom, but in the administrators office. He threw another one of his Monkey boy style tantrum. Apparently he wanted to be line leader. At my sons school you are only line leader for the day if you parent is the Helper for the day. Well his favorite girlfriend was the line leader and he wanted to "share" the spot with her. This is not allowed. Monkey boy ended up being the very last one in line, and when the began to walk down the hallway to go to the playground he tried to cut in line to get closer to his friend. The teacher grabbed his arm and "tried" to bring him back to his spot in line. This then prompted Monkey boy to fall to the ground. I do not need to explain what happened next, anyone with a Toddler or Preschooler knows. When I picked him up he was crying and the administrator told me that its hard for her to believe that this is coming from a 5 year old. She told me she has seen this with 3 & 4 year old's,but not with someone who is 5. I replied "well he just turned 5 last month". "Nothing excuses his behavior,but he just turned 5" I asked Monkey boy to say he was sorry for his actions, and I could not get him to talk. I apologised for him and we went on our way. Later that night I talked to her again on the phone. She told me that Maybe if I followed thru with my discipline he would start to behave better. "What?" "Excuse Me" Anyone who knows me knows that I follow thru. I was a bit offended by this comment. She then went into detail about how I could not get him to say Sorry . I explained to her that getting a UN heart felt apology from my son at that time was teaching him nothing in my opinion. I told her I did not push the apology from him because I felt like he had enough discipline for the incident. Having been in the office for 45 min and missing snack and recess. I then told her that this situation is not over in my book, we will be writing another letter of apology, and he will come back and say a hart felt apology the next school day. I also informed her that he has had a hard year thus far, a new baby, a new house, and we recently had to get rid of our dog of 8 years. I told her none of this makes his behavior appropriate, but he might be dealing with all this in this negative way. The thing that has me upset besides the obvious behavior issue is that he was in the office for nearly 45 min. Why wasn't I called? I feel as if I should have been called after the first 5 min if he was not calming down enough . I will let the Preschool Coordinator Lady know that if this is to ever happen again I want to be called right away, because I think sitting in a office for 45 min is too long for a 5 year old. I am wondering what the rest of this school year will bring. Boy this Parenting stuff is so much harder then I ever expected.