The dog's carrier fit under the seat, which is the accepted requirement for pets riding in the cabin of an airplane. Anyone working on aircraft should know the overhead bin was not meant to carry living creatures, plus a look at the dog's face could tell you he might have breathing issues.
Absolutely stupid thing to do, order the dog owner to do that!
The airline, of course, has apologized, for all the good that does now.
--------------- Von Konigswald: Jack the Ripper plays shuffleboard. -- Happy Birthday, Wanda June by Kurt Vonnegut, c.1970.