It's because the Rwandan learned from one — a French book called "The Secrets of Swimming Development." And only from the illustrations — Niyomugabo doesn't even read French.
"My main coach all my life has been this book," the 24-year-old Niyomugabo, a two-time Olympian, said in an interview back home recently, referring to his precious swimming guide.
Coming from Kibuye on the shores of Lake Kivu, Niyomugabo swam from a young age. But to develop a proper style and speed, he needed the textbook that was given to him by a high-school teacher, after Niyomugabo made a name for himself as a swimmer as a teenager.
That book and his TV became his two most valuable tools in his quest to go from an undeveloped lakeside town in east Africa to the Olympics. Watching top swimmers competing on TV, Niyomugabo would compare what he saw with the illustrations in his book. He would constantly glance back and forth from television to book, making mental notes and planning to put what he'd seen into action when he trained later alongside fishing canoes on the shimmering lake that separates Rwanda from Congo to the east.
"It was an extremely difficult way to learn," the 50-meter freestyler said. "I would sit for hours in the hotel lobby staring at the TV. And when I swam I didn't even have someone to hold a stopwatch to tell me if I was improving."
His story is reminiscent of Eric "the Eel" Moussambani, the Equatorial Guinea swimmer who made such a splash at the Sydney Olympics for being, well, really bad. Moussambani practiced in hotel pools and in a river and won over the crowds in Sydney with his determination to finish his heat despite struggling badly.
Niyomugabo learned enough from his book to go to the Beijing Olympics in 2008, when he failed to get past the preliminaries. He's back four years later and hopes to improve further in London.
"I want to win a medal this time," he said, wearing a four-year-old blue and yellow Rwanda team uniform from Beijing and lying on a sandy beach outside the hotel where he offers swimming lessons. "And why not? After all the things that have happened to me anything is possible."
It is an outrageously unrealistic goal, with world record-holder Cesar Cielo of Brazil, Australia's James Magnussen and American pair Cullen Jones and Anthony Ervin — to name just a few — way ahead of the Rwandan. Niyomugabo's qualifying time was around six seconds slower than the leading contenders in swimming's quickest Olympic race.
He starts in London on Thursday in the 50 freestyle heats against swimmers from Sudan, American Samoa and Djibouti and will have to improve drastically on his times to progress to the semifinals.
But, just having a swimmer at his second Olympics is undoubted progress for Rwanda considering the bare facilities and resources available.
In fact, there's two swimmers on Rwanda's seven-member team in London with 16-year-old Alphonsine Agahozo set to compete in the women's 50 freestyle.
In the absence of a permanent coach, Niyomugabo has relied more on natural ability than any finely tuned technique, he said.
"If I had more support I am sure I could swim faster, but this is reality," he said. "In Beijing I was very young. This time I am training harder, and I hope I will see the results."
Niyomugabo was discovered seven years ago when he won a local race by some distance, but his only coaches have been temporary and stayed with him for just a month around major competitions.
This week, the thickly vegetated islands and hovering black and white kingfisher birds of Lake Kivu give way to the cavernous and sleek new Olympic swimming venue and thousands of roaring fans.
"He is very gifted, a self-made man," said Richard Ramira-Lema, Niyomugabo's coach at the Beijing Olympics. "Without a regular trainer or an organized club he has made a leap. If he is more disciplined he could do well in London."
Ramira-Lema's reference to indiscipline referred to his struggle to keep Niyomugabo away from hamburger fast food restaurants at the last Olympics, something the swimmer will need to conquer this time.
"Given his background it was natural to be tempted by such food," Ramira-Lema said.
AP Sports Writer Gerald Imray in London contributed to this report.