I looked at this quote in a slightly different way. If one writes a story every week, it means he/she is writing consistently. I'm a firm believer in writing on a regular basis.
I'm sure there are people who can write nothing for six months, then sit down and dash off a story that is publishable. I also think that those people belong to a very small group. The rest of us need to write often.
Athletes work on their skills day after day. They exercise. They try new ways to hit a ball with a bat or get a basketball into the hoop or throw a longer pass. They work on their skills even in the off-season.
Musicians and singers don't play or use their voice only on occasion. They practice a lot. As do circus acrobats and long distance runners and artists. We writers are no different. To polish our writing ability, we need to practice it often.
One day last week, I was playing Bridge and my partner surprised me with a question out of the blue. "Do you write every day, Nancy?" she asked.
I hesitated a bit before answering because the question was unrelated to anything else we'd been talking about. I told her that I do write something almost every day. Writing this blog five days a week definitely counts. I might write a personal letter or a journal entry or a writing exercise. I also do several critiques of other peoples' writing and that counts as writing for me. Sometimes my writing for the day takes hours while other days it's minutes. But, yes, I do write nearly every day. Even when on vacation! I usually keep a travel journal so put my thoughts and the events of the day in writing on a daily basis while away from home or I write my blog in a hotel room when we travel.
One of the reasons I continue my blog is that it does require regular writing. I will admit that sometimes it takes time away from writing a story or personal essay. When I'm working on another writing project, I increase the time I write that day.
Hone your craft by writing something every day. Even if it is only 15 minutes. You won't regret it. You might even take Ray Bradbury's advice in the poster quote above. You may strike gold with some of those stories.