So what takes so long? I assume their process is roughly "consider all possible moves, decide how good they are". So if they only look one move ahead, that sounds to me like when they evaluate a potential position, it can take more than a few seconds and they do it without reading possible future moves. Which seems unlikely.
Am I misinterpreting "one move ahead"?
He's being witty, is all.
"As time goes on, your thought process will start to be based more and more on your positional intuition. Instead of explicitly weighing certain details against each other, you will instinctively be able to feel what direction the game is headed in. This intuition does not come naturally, but instead is the result of playing hundreds and thousands of chess games. Over the course of all those games, you will see positions similar to the one you are playing right now, and even though you may not explicitly internalize them, your subconsciousness will recognize the themes from before, and you will have some vague recollection or understanding of the position based on your prior experience."
IIRC, in phase one, experts see wo or three moves to look deeper into. Non-experts see many more.
I recommend reading "het denken van den schaker" if this interests you. It is very readable by laypersons (and a translation in English exists)