Why do people say being gay is not a synonym of being effeminate? some gays could be very straight? how is tha

I still dont get the point.. but all gays I have seen in my town.. in mexico.. they are effeminate.. even the gay shows gays with straight qualities. I dont know if they are gay or bi.. I am supposed the bi guys are straight.. because women would not like an effeminate guy right? I know some guys still dressing like a man. etc. but they have effeminate things in themselves..why does being gay is related with being effeminate?if they are gays very straight how do you detect them?