Inaccurate, this account; the bombs, not so much. The aiming point for the Hiroshima bomb was the the Aioi Bridge, at the juncture of the Ota and the Motoyasu Rivers. The detonation was roughly 1890 feet above, and 800+ feet south-east of the bridge. As TIbbetts said, best aiming point he’d ever seen.
Your description sounds like you are thinking of Nagasaki. In which case it is wrong, too. The Nagasaki bomb did indeed fall 1.75 mile+ or so off from the original planned aiming point. That was a result of the cloud cover, complicated by the fuel problem Bocks Car had experienced, from the start of the mission, through the aborted bomb runs over the original target, Kokura, and the final attempt to locate the alternate aiming point, over an obscured Nagasaki. The result put the bomb hypocenter closer to the industrial areas along the river, and allowed the Urakami valley to protect the more populated areas to the south east from the explosion. Lives were, in fact, saved by the miss.
Neither bomb used a parachute deployment. That would completely degrade the idea of accurate location of the detonation, which was essential to the maximum effect. The drop time from altitude was (memory says) in the 45+ second range), and the get the heck out of Dodge technique Tibbets had designed, a 150+ degree descending turn, fire-walled,put the maximum slant range between the planes and the explosion. At Hiroshima, that got ENOLA GAY roughly 11 miles out, before the shock wave over took them. Adequate.