As others have said, as long as the first name and last name are correct he can relax. I usually take care to make sure that the ticketed name is exactly the same as my passport name (especially when flying to/from the US), but forgot to do this when I flew BKK-LAX-BKK last month. As a result my middle name was missing. There was no problem at all (other than the immigration guy in LAX giving me the benefit of his opinion at some length of why the US lost its AAA S&P rating, but that's another story...)