Just a word on the positive behavior modification plan you started at home. That is great for things he does at home. Virtually useless for things that go on at school. He is too young to deal with long term (for him) cause and effect.
My son is 4 and a half and was having the same problems and worse. I actually put him in the last two weeks of Summer classes because I thought this could happen this week. So, I had time to work on his problems before the year started. He did have serious problems in the Summer (and he was a pre-school student in the same school the year before). Ffor the first time since he was potty trained he also had 3 accidents at night. I had a meeting with the teachers, explained what I thought was happening to him. They became more aware and patient. I explained what helps him to follow directions (certainly not getting mad at him, which only increases his anxiety -- he was very anxious about going to school). I also wrote them notes explaining potential triggers of tantruns (e.g. he gets very angry at other kids who try to get whatever he is playing with). Finally, I took him to a developmental therapist. The result has been excellent. He is learning social skills, how to deal with the other kids (kids his age can be very aggressive and do not have a good sense of boundaries, which makes him very upset). The teachers are saying that the difference is night and day. In your case, your son was doing well before, so I think you need to talk to him, see if you can get him to open up to you. Tell him that it is ok to be anxious. And talk to the teachers -- be an advocate for your son, as only you can understand him and will put the time to figure out what is going on (and a therapist, but I do not think your son needs one)
probably, maybe make an appointment to talk with the teacher. the more involved you are the better he will do. it is probably just he is curious and maybe forgot to listen. i would just keep on top of it, be friendly to the teacher and show your concern that he do well. he liked his preschool and so it is a change for him everything new. hopefully he will like kindergarten too.