As an attorney, I actually handled such a claim a few years ago where an injured passenger was making a claim that a business traveler from my employer dropped luggage from the overhead bin. I looked at the various legal issues (don't remember what state since this is a state law issue) and thought it was a pretty open and shut case against the employee, and that we were liable because the employee was engaged in business travel. We paid the claim, although it wasn't much.

Here, I think the case against the woman is pretty clear - we all have a duty to check that we aren't causing an avalanche of luggage when pulling things out of the overhead bin. I don't think the answer is not to carry things on. In my experience, business travellers use carry on's that are properly sized and can be easily stowed in the overhead bins. OTOH, some travelers travel with oversized luggage that is too heavy for them to lift into the bin.

Glad to hear your son is OK. Thanks for sharing this - I'll be more careful next time.