When we had an incident at school, (a teacher posted something on facebook), the parent was told that there had been a review of safeguarding procedures, and a training update. It meant the teacher had been bollocked and the HT had reminded the whole staff about the policy wrt FB and social media.
As a governor, I know that was what happened, the version to parents was the professional version of that. As a governor, I was satisfied that the HT had done enough to ensure it didn't happen again. If I wasn't satisfied of that, then the governors would have taken it up with the head.
As it was we did grill her a bit to make sure it had been all covered and properly dealt with and wouldn't happen again.
Unfortunately you will not know all of that, you can only know the professional version (for want of a better word). But if that includes that she has taken steps to ensure it won't happen again, well, you have a choice, believe her or not.
If the head has had a word with the teacher, then the teacher would be incredibly stupid to do anything which is a repeat of this.
For me, an apology and a reassurance that the head has dealt with it, would be enough, unless my child had the same teacher next year, and then if I really felt it was malicious, I think I would ask for my child to change class, or if that isn't possible, I would consider moving.
I have to say though, most teachers are too professional to be doing this chinese whispers thing with intent to be malicious, it just sounds as if there was a careless mistake.