In my experience, the “I’ll just find a new job in a week “ meme is overstated. It takes longer than a week to get to an onsite interview in my experience. Sometimes it’s even longer.
Admittedly yes, especially in the current market but it does illustrate the reasoning behind the quote. The shift in labor-market power of developers is undeniable. Realistically it would take me closer to a month from search to first day if I was jumping at the first opportunity. I've certainly known people with a broad enough network and in-demand skills who could land one in a week or two however.