I'm not a fan of pets being dressed up generally, but I think this is a group of dogs and their walkers who enjoy their meetups. When we had dogs, we were part of an informal meetup group, and both dogs and their owners enjoyed the socialising.
I think in this instance, all participants would have enjoyed the occasion, especially if the canine participants were suitably rewarded for their involvement! (my dogs would do anything for a treat, and then demand an encore)!
So this instance I think was a daft but light-hearted nod to the festive season.