It reads to me that this was a delayed service from the previous day, carrying the delayed flights 300 pax, not a new or mixed uplift and not a normal schedule.
Yes unfortunately staff and crew do have to take everything with a smile, not fair but that's life and good customer relations. Will that customer and the rest of the passengers have good feelings and customer loyalty re VS in the future, I doubt it.
Change the scenario to any other service industry or even govt. office, if someone complains you have to deal with it sensibly and with tact and servility whether or not the complaint is due to something you have done or not...
Being in aviation just doesn't change the fact that it is a service industry and customer service and handling are vital to a smooth operation (or should be!)
Just because you are being piled onto a metal tube doesn't mean to say you (as a customer) have to accept being treated badly...although as discussed before concern for the customer seem to be on an ever increasing slide with some airlines.
Yes bad situation...handled badly and made worse by a staff member.