Why does Tom's behavior seem strange in The Prince and the Pauper?

Tom Canty was born in a poor family. He was expected to beg for alms in the streets in order to supplement the family’s income; if he failed, he would be thrashed by his father and grandmother. He spent most of his time listening to Father Andrew, who told stories about a dreamlike world that only offered wonderful experiences. The stories offered Tom an opportunity to unleash his imagination. He started to explore the princely life which had such a strong impact on his character that he carried himself as such. His mannerisms and behavior resembled that of members of the royal court.

Finally, he got an opportunity to live like a real prince. However, all he had learned outside was not enough.

His old dreams had been so pleasant; but this reality was so dreary!

His lack of knowledge about princely duties and specific procedures concerning the royal court made him behave strangely.

Tom's next unconscious blunder was to get up and leave the table just when the chaplain had taken his stand behind his chair and with uplifted hands, and closed, uplifted eyes, was in the act of beginning the blessing.

He was unable to answer some of the questions, like the one asked by Lady Jane about his duty to the Queen.

“Hast paid thy duty to the Queen's majesty to-day, my lord?”
Tom hesitated, looked distressed, and was about to stammer out something at hazard, when lord St. John took the word and answered for him with the easy grace of a courtier accustomed to encounter delicate difficulties and to be ready for them—

Except for the basic Latin that he knew, Tom was completely out of place, and according to members of the court, he was going mad.

“Now were he impostor and called himself prince, look you that would be natural; that would be reasonable. But lived ever an impostor yet, who, being called prince by the king, prince by the court, prince by all, denied his dignity and pleaded against his exaltation? No! By the soul of St. Swithin, no! This is the true prince, gone mad!”