"Bullish in gold, but only in Yen terms" means that he thinks gold will go up against the Yen, but not against other currencies. The translation of this is that he thinks the Yen will go down. I'm not sure why he chose to phrase it like that, unless he is in the business of selling gold.
If you sell USD to buy Yen, and then use that to buy gold, that ends up being exactly equivalent to buying gold with USD, less a couple of extra transaction fees. If this commentator's predictions come true, then you will be able to sell your gold and buy more Yen than you started with. Unfortunately, you will lose all that gain when you convert your Yen back to USD. And you will pay extra transaction charges when you sell.
Unless you want to keep your money in yen after selling gold, then this advice is irrelevant.