House has agreed to a "date" with Cameron (not just a dinner between colleagues).

House had agreed to go on a "date", not a dinner with a colleague. He then had the problem of trying to figure out what would make this an actual date so that he could live up to his agreement. Since we can see by his behavior that he had no plans to sleep with her at the end, he had to do something. So, he wore the shirt Cuddy told him made him look nice. And he took Wilson's advice on complimenting her shoes and earrings. He also made a reservation at a nice restaurant. He dressed up, when he rarely wears a tie, etc.