I'm not sure what all the foreigners attending the event would make of an aged cold-war killing machine overflying them. What possible relevance to the celebration of one of the world's top sporting events would that have to them.
Nice for the Brits, if some of them knew [or cared] what they were seeing, but to everybody else, zilch.
Well one or two Vulcans acted as test beds for the Olympus engine - that's relevant, surely?
More seriously, you may as well say that any flypast is irrelevant to the opening of the Olympics. But if you are going to have one, then a big noisy beast like the Vulcan will make it all the more impressive.