According to this article she got other parents’ experiences and their kids were not suspended. I guess that is proof enough for me.
Not sure if you're being sarcastic, so I'll just go ahead and play it straight: we don't know the full story. If that other kid threw something and it was the very first time he'd ever gotten in trouble, that might be a factor. We don't know what he threw, either. Eraser? Not quite the same as a chair. Does her child work the teacher's nerves relentlessly all day? Might could be so, yes? I'd just want to know more.
I still don’t know enough. Are the other kids constant pains in the rear, or was their misbehavior a one-time thing?
Are the other kids always smarting off, or are they generally nice and well-behaved? What about the author’s kids? Are they generally well-behaved?
If two kids throw chairs and one is always in trouble, but the other never is, they deserve to be punished differently.