I know that story and I have severe doubts. The sources is Wroth, a contemporary biographer of engravers. Pistrucci receive much criticism in London. Forrer says that it was mainly because he was a foreigner: "Pole offered Pistrucci the post of Chief engraver. The appointment was resisted by the moneyers (the corporation of the Mint), and for several years Pistrucci was attacked and calumniated in the "Times" and other newspapers, chiefly on the ground of his foreign origin. "Among Pistrucci's chief opponents were Mr. Hawkins, the Keeper of Coins and Antiquities at the British Museum, and Nicholas Carlisle, Secretary of the Society of Antiquaries. The artist's works were described as having a scratchy appearance, and of wanting in boldness ; he was reported to have cut the steel matrices by means of a lapidary's wheel, and practically accused of extorting money from the Master of the Mint. Carlisle's aspersions were refuted by W. R. Hamilton (William Richard Hamilton, vice-president of the Society of Antiquaries), who broke friendship over the quarrel."
Pistrucci was of course a child of his time. Classical art was fashionable and so were (preferably, but not necessarily, naked) gents on horses in funny positions. There are paintings of Napoleon very much like the St. George Pistrucci made. However, it would be unfair to Pistrucci to say he copied this or that work. He merely made what was fashionable. Of the St. George, Forrer says: "The jasper George and the Dragon, purchased by Wellesley Pole for the coins, was an original, and not the cameo, or wax model, which he had made previously for a 'George' to be worn by Earl Spencer, K. G. The design was considerably modified, and the St. George was modelled from life, the original being an Italian servant in Brunei's Hotel."
There is more to another story. Pistrucci wanted his family to come over to London, but the Mint refused to pay for the removal. Pistrucci got paid for a die never used so he could move his family. Forrer has most of the story: "To remunerate him in lieu of engraving gems, the Master of the Mint hit upon the expedient of ordering the Waterloo Medals, as an extra work, for the execution of which it was agreed that he should be paid three thousand, five hundred pounds sterling, the sum of two thousand pounds being advanced to him by instalments within a short time (Billing, The Science of Gems, Jewels, Coins, and Medals, Ancient and Modern, London, 1875, p. 193)
The Waterloo medallion, the dies of which were never hardened. though impressions in soft metal and electrotypes were taken and sold to the public, far excelled, according to Pistrucci's own published account, anything ever attempted in that way both in its magnitude (4 1/4 inches in diameter) and likewise in the number of the figures introduced.King states that it had been originally the intention of the Mint to present a copy in gold to each of the princes who shared in the triumph, and in silver to the minor satellites ot their glory. Tempora mutantur. The dies lie in the Mint Museum."
Actually, the Mint realised it did not have the equipment to strike the medal. This may explain why the dies were never hardened.