He is sore because his scam/false advertising has been found out. It is now publically known that he can't be trusted, and has lost alot of potential business nationally.
If evidence could be provided and he was up front and honest, plus treated people with some manners then I would believe he is a true business person. But his wording and manners suggest that he has obviously been short changed in the IQ department, especially thinking he could scam an Skyline car forum that he actually has a legit NISMO tunned/built engine in a GTR.
If he was serious, then paper work, dates of work done, updates to FAST and NISMO themselves would be able to verify the said car. Alas this has not been case, and as a business person I would have expected you to have fully researched the vehicle before importing or selling. So in the end it sux to be u!