The callers thought that they were being ridiculous - they thought that their accents and use of language and so on were so obviously daft that they had no idea they would actually get as far as they did. They thoguht they'd call, say some silly things, and have people laugh at them for being so inept at impersonating royalty.
Tragically, working for the modern NHS is for many people a stressful unpleasant experience with a lot of management and bureaucracy.