I've seen reference on discussions of accidents to "get it in itis" or a similar phrase: pilots who have established a plan to land the plane on this runway on this approach, and become fixated on that task to the exclusion of alternatives (go around, divert) as conditions change.
I suspect that's what happened here. A stressed member of gate staff, confronted by four flightcrew who were claiming rights that they may or may not have had but that the gate staff didn't feel able to gainsay, became focused on "I need four seats, this is one of the seats I need, therefore I need the police" rather than looking at other ways to resolve the situation. Their cognitive fixation was completely "clear seat 26B". That people do unreasonable things to achieve one goal without thinking if changing goal would be better is hardly news, and something that the airline industry of all places should be aware of.
The claims that airlines are limited in what they can offer are nonsense: passengers are limited in what they can claim in compensation for involuntary non-carriage (both in the EU and the US, certainly); notably, they cannot claim consequential loss in the vast majority of such incidents. But if an airline is looking for volunteers, because it's better
PR, they can offer whatever they want. They may well have internal policies which limit the discretion of individual staff, but that is their internal issue.