The event is "formal." Formal means tuxedo, otherwise known as black tie. Notice in the pictures of the honor guard, that they're wearing short jackets. They're not tails, but they're the Scottish "Prince Charlie jackets." (http://www.scotweb.co.uk/products/classic-prince-charlie-jacket-and-vest/) The bow tie is standard with tuxedos. Some of the guys have ties in their tartans, which match their kilts, of course.

Me, I'm just wearing a suit. Not formal formal. But they weren't going to kick me out.

See Black tie (https://en.wikipedia.org/wiki/Black_tie).