Arcturus, of course, was quite fervently patriotic in the ways that mattered, but he also knew that adults didn't tend to be outspoken about such things. He hadn't taken the remark seriously, because who wouldn't want to be British?
He managed to keep a straight face as John Smith introduced himself. Yes, there was a chance that he really did have such a common and forgettable name, but it was far more likely an alias. Not that it mattered. Arcturus could see the sense in not giving one's real name in a place like this. He was wary, but not afraid – muggles weren't to be trusted, but he had his wand tucked safely in the inside pocket of his jacket, so he wouldn't come to any physical harm, and having muggle paper money stolen, or being tricked out of it, wouldn't trouble him over-much.
'Then it's good to meet you, Mr Smith, and I must thank you for your hospitality,' he said then, leaning back a little. 'It's almost a pity that I told my wife I'd be home soon. She really-'
He was saved from a continuation of the lie by the return of the waitress with their drinks. 'Ah. There we are,' he said brightly.