Unfortunately I think these kinds of incidents are going to become more commonplace; air travel continues to become a more unpleasant experience every day and it's the airline employees that face the brunt of it. Is it any wonder that they're losing their patience?
Other's mentioned that this lady would have been informed about her buggy at check-in. These days, many people don't even go to a check-in desk. Online check-in means that people turn up at the gate, without having seen an airline employee. The gate agent (often working alone), is expected to check boarding passes, look for oversized cabin baggage, check visa requirements and label mobility aids of 180 or so passengers, under the constant threat that they will be held accountable for any erosion of on-time performance.
While airlines continue to cut costs and staff, it's the frontline employees that feel the pressure. It's easy for us to say that this incident should have been dealt with differently, but the guy is human. Imagine dealing with this nonsense day in day out, week after week.
The travelling public have changed considerably in the last 10-20 years that I've been flying as a passenger. People are much more self entitled, less considerate and if they don't get their own way, they throw a tantrum or threaten legal action. People refuse to follow simple instructions, and think that because they have seen this, that or the other on the internet they are suddenly an expert.