The thing is that pronouncing it "JIF" is NOT inconsistent with its spelling. If you just see the word spelled out, in the English language the pronunciation is ambiguous. Therefore, the inventor stating that it is pronounced "JIF" is perfectly reasonable on all accounts. If he tried saying it was pronounced "DIF" or "LIF" or something, then sure--I'd be skeptical and probably still pronounce it the way I think it should be pronounced. But "G" can make the hard "G" sound or the "J" sound, so it makes perfect sense for the inventor to say it's pronounced "JIF".