Most will say it's both.
There are truly great legit players who can and will birdie just about every hole.
There are also cheaters.
For the legit players it takes lots of practice, mapping your clubs so you know exactly how far they will hit your ball, and knowledge of all sorts of other aspects of the game.
Most who shoot those really good scores are great putters and so when that approach flies just a bit longer than expected, they sink them anyway.
It takes lots of practice. Also utilize the forums (search), there's lots of information on how to get better and don't be afraid to ask questions. There are lots of people who frequent the forums who will help.