I think that the answer "Я ТВІЙ офіцянт" should be accepted as well
That's grammatically correct (but it is "офіціант"). But that not a sentence that you can hear that often, because офіціант definitely won't be referring to his clients using informal form ти
And I guess if it's a group of підлітки out for a bite to eat he'd still use ваш because it's a group of young people. If your customer is one teenager does the formality change to ти?
I haven't been to restaurants as a kid/teenager, so I can't speak from my experience, but I don't think it's appropriate to use ти. They are clients, that's what matters
This is exactly what was given as the correct answer.
yes its a bad - very unlikely - sentence to use.