Sinclair's forecasts over the last decade have been hopelessly wrong. Of course gold is in a bull market, that doesn't make him a genius! He is the one who crashed the gold price in 1980. He is very heavily invested in gold and gold mining, so he has a very good reason to pump it.
Anybody investing in gold on Sinclair's advice hoping for a quick buck is likely to be disappointed - it has a long way to go yet.