Watch it first and then see if you agree with me here.
My favorite parts, which prove that it's not just about write what you know but rather notice the details and tell them true, are these moments: when he holds up a heart-shaped paperweight and says, "This isn't my desk, by the way"; the twist that at 13 he wrote this piece to stick it to his teacher by making it as deeply boring as he could; and when he says the old lady's home smelled "of tea, and lavender, and mold". How much do you learn about him and the way he sees the world just because he picks up that paperweight and laghing, says those 7 words? And about his character as a 13 year old wise-guy kid, from that goal of his? Especially combined with his comeuppance and his declaration of how proud he was to have failed at his goal but succeeded at something deeper? And finally -- wow -- can't you just SMELL that old lady's home? Those 3 smells combined in his 13-year-old wise-guy kid's nose? Tea, and lavender, and mold. It's not a cliche. You never heard somebody's home described like that and he didn't need to tell you square footage or socio-economic situation or what color was the wallpaper. He got right to who that lady was, and how he looked at her, his whole experience sitting there bored and miserable. He deserved that A. As he later says, "being honest is what counts. Trying to make the ordinary extraordinary..." So it's not just "write what you know" but rather: get to the honest stuff, the truth (and the best way there is through the weird true details you notice or invent, and then invest with attention) -- that's what makes good writing.
And hooray for excellent teachers, who push us to do better than we think we can.