Not really “one in a million”. A shot like that takes a lot of planning. You don’t get a pic like that from luck.
You can line up a shot to have the moon set behind any feature near the horizon any day on which the moon sets. There is a cell phone app for that, called "planit", I believe. The challenge here was to find a date when the moon was setting aligned along a particular azimuth, determined by the line of sight of two landmarks. He probably had noticed the alignment of landmarks before he even thought about the moon. By my calculations, he had about six seconds to snap the shutter to capture that near perfect alignment. He almost certainly worked out the exposure long in advance with practice shots on days with the moon to the left and to the right. And of course he probably took many bracketing shots before and after the magic moment to make sure one was spot on.
As my calculations, described above show, the moon presents itself like that about once every 2400 days. Six seconds in 2400 is about one in 34,560,000, so far less one in a million, if you just continuously snap every six seconds. Accounting for weather, and lunar phase, roughly once in a lifetime.