It has to do with the attitude of the English towards the Irish - especially in 1964.
So a young Irishman without credentials and without funds arrived in London and then he was able to quickly raise a lot of money and get involved with many different commercial ventures, except that he lied. He did none of the things he claimed.
He took fractions of truth and turned them into enormous lies because he was paid to lie. That is how he made his money. He was a paid con man.
But, back in 1964, if a young Irishman walked into a bank and asked for a loan for anything, he would have been shown the door - or thrown out of it.
Nowhere did O'Rahilly claim the excuse you are now raising for him. Besides which we now know that he was a fraud and we know who put him up to it, and why. See today's companion Blog.