Is it true? Is becoming a writer as simple as sitting the wondrous ass in a chair and writing word after word? Yes. And no.
A lot more goes into the trade of writing.
First, you will also need to do some reading. No, wait. I mean A LOT of reading. Why reading? Because that is how writers learn how to write. It is where we discover how people interact in books, how to create casual conversations, drop plot hints, and create a mood.
Writers also study grammar to some extent. We know how to form sentences, spell most words correctly (and use a dictionary when needed), and we know which rules we can break.
As a writer, you will also need to develop a thick, resilient, super-duper strength hide. If you plan on finding a literary agent, prepare to get turned down. If you are submitting your work to publishers, prepared to be turned down. If you are self-publishing, such as on Kindle, prepare for readers to read your work and hate it, hate it, hate it. Your family will not understand why you want to be a writer. The people you love will tell you to "get a real job." In fact, the life of a writer can get old real fast.
To become a writer, you will also need an astounding amount of determination. After all the rejections and the people you care about poking fun at you, you will still need to write and share it with the world, no matter how many people hate you for being you.