I think that is reasonable, and if I am not mistaken, most schools have incident reports that are internal documents that they keep when ever a child is injured at school, for thier own legal protection, and it just seems logical that they would also notify the parent of the incident.
I have an odd perspective on this, as two of my autistic children attend a charter school for kids on the spectrum, and in my opinion, that school is much less apted to send me a notificiation that something has happened to my child at school, because they handle everything so well, and I don't worry about it much.
The public school my typical child atteneds has a more hit and miss record. Sometimes they report, and sometimes they do not, and it seems to me that they report when they really know it was something to take seriously, or when the actual nurse is the one who saw the child, and sometimes, they just don't think it was a big deal, or the person who gave them the ice pack was a sub, or a secretrary who does not know that there is any need to notify, when the nurse would have more experience in knowing when to do so. It is hard to tell sometimes what really happened, and if the ice was a for the child's injury, or if the incident seemed to the nurse or to who ever gave out the ice, to be more of an amusement. One of my childre was a regular in the nurses office, and you may not know if your child fits into this group. They really are different at school than they are at home. Not suggesting anything here, just that kids are kids, and stuff happens, and teachers and school officials are imperfect and don't always see what we want them to everytime.
If you think it was a true injury, and that you should have been notified, by all means, find out what the policy is, and let them know that one slipped by, but take into account all the other stuff that could be going on here too, the nurse, and your teacher will both aprreciate that!
M.