Why is the long-run average production cost not necessarily the same as the minimum average total cost? As you can see from the graph, the LRATC doesn't touch the SRATC curves when they're at their minimum. Why is this so?
Denesp's comment is your full answer: it's a badly-drawn chart which fails to do its one job, that was to illustrate that the long-run cost curve consists of joining up the minima of the short-run cost curves.