If the crew directed the passengers to sit on the floor or did not give gem the opportunity to sit in other jump seats during the service period, then they have a problem.
Pax using jumpseats is fine, but they need to be shown to them and shown how to use them, not just have it assumed that they know where to go and what to do.
The key issue is who directed them to sit on the floor? If the pax were shown to jumpseats and chose to sit on the floor themselves, then there is no issue. However, If, as the article suggests the crew asked them to vacate their jumpseats in the galley and then did not direct them to jumpseats elsewhere, then that is where it all falls down.
No-one is going to gaol over this, but there should be some uncomfortable meetings and some updated procedures and courses.