Streets ahead

My piece on Harry Mathews begins:

On June 19, 1997—a few weeks shy of my 27th birthday, and fifteen years nearly to the day that I am writing these words—I stopped by Book Ark, a used bookshop three steps below ground level on West 83rd Street in Manhattan, and bought my first Harry Mathews. 

It should be noted that Book Ark was on West 81st, not West 83rd!

The first footnote in the piece runs:

Or was I indeed already living in the tiny studio on West 81st, putting me within two blocks of my goal?

But I was living on West 83rd, not 81st! What does it mean that I mixed up the streets?