It was always composed of tiny moments.  I wrote the original version for a Kathy Fish workshop.  I think the assignment’s word count limit was 150 words, and my first draft was probably 250-300, made up of brief sections.  For the assignment I sweated this down to 150.  When I came back to it a month or so later, I resurrected some of the words I’d cut, as well as adding new material.  I’m drawn to shorter forms at least partly because I tend to write in small units, a couple of paragraphs at a time, afterward stitching the pieces together to make a whole.  With a story like this, rather than expand and connect the fragments, I condense them, the goal being to present only the most concentrated and vital sections.  And then as you point out to let the reader fill in the gaps.