It was much too early for the meeting
Attending a meeting in casual attire and arriving early is quite acceptable. In this example, seeing a customer where they are most comfortable would be fishing in their undies. There is nothing wrong with it. But if you show up to a meeting early in the morning and without trousers, you may want to reconsider some of your decisions.
However, that briefcase exudes both confidence and professionalism, and that’s something to be proud of.