The author is merely addressing the logical consequences of inertial effects on space travel. No one will ever travel to Alpha Centuri in four years. Even the fastest probe ever created will probably take centuries to get there, but may send back photographs that arrive in four, if there is anyone around who remembers to look for them.
Yes that’s true enough. But even at 1g acceleration and deceleration the whole way, it would take about 6 years. But that would require insane amounts of energy. More that 1g would be additionally insane.