If someone has 1 bitcoin cash, does he also gain 1 segwit2x??
No, if that happens then a lot of people would be buying bitcoin cash right now. You only get the forked coins depending on how many bitcoins you have in your wallet. Also having 1 bitcoin gold won't gain you 1 segwit 2x. 1 bitcoin is not the same as 1 bitcoin cash or 1 bitcoin gold.