I think Delta might have assumed they could get the seat, then got their backs up when challenged.
More than likely what happened. Naturally, you don't dare challenge airline employees, comrade!
I'm sure the Freeper "Rulz Iz Rulz" boot lickers will have a field day with this one.
Incrementally over the years it appears a growing portion of posters on this site are unconsciously drinking the kool-aid of not questioning authority and accepting whatever fate is decreed.