After the bitcoin gold fork there was a slight drop on the price of bitcoin, from $5900 to $5400 but as of now 2 days after the fork prices are ranging from $5800 - $5900 again. So it is safe to say that BTG somehow affected bitcoin's price because the people who hoarded bitcoin to get their BTG tried released it at the same time after the fork but the market is stabilizing at a higher price now.