Most of my 13 yrs of substitute teaching has been in 1st and 3rd grade.
Granted, 1st graders need a lot of nurturing and hand holding to gain confidence with their skills. First grade is my favorite, I love them.
That said, I have seen some deplorable behavior with first graders and I have seen teachers speak sternly (not yelling) to the class. How else will the teacher maintain control of the classroom?
We set the tone as a loving teacher but we also have to set the tone that we are in control of the classroom. It is expected that the children be respectful to any guest in the classroom as well as behave appropriately in music, PE, art, library, cafeteria, guidance counselor, etc. Disrespectful behavior in these areas do constitute a consequence such as some time out of recess to think about the behavior. We also ask them specifically... what would your parents think about this behavior right now?
Hopefully, your child's teacher had a bad day. Everyone has a bad day now and then and I am not in favor of yelling at a classroom of 1st graders or any student.
I have given clear and specific instructions for a project and have 1 or 2 children in the class think it is 'funny" to disregard the instruction. That type of behavior catches on with others as one child will giggle, etc.
It is funny, when they sometimes act like this with me, I take the project and I let them know that their teacher will love to see it. Talk about regrets when that happens... I've had students cry and beg me not to show the work to the teacher. So I ask, why not? Is this not the quality work you do for your teacher?
We encourage creativity, we demand quality work. I don't care if a reindeer if purple.. if a child did his/her best.. that is what matters.
I would let this go. If you can possibly work out the time... go volunteer in your child's class. if and when you do, you will get a good feel for the dynamics and see if the bad day is a rare thing or daily thing.