Someone asked me about this so I poked around a little, including on the now-closed thread we had going about it last year. It's classified as 'straight whiskey,' which is a classification you rarely see, and assuming the increasingly dubious proposition that TTB applied the rules correctly, that means it's probably a mixture of straight whiskeys of different types.
The producer (Western Spirits/Three Springs in Bowling Green) says it contains bourbon so my new theory is that it's a mixture of bourbon and straight corn, which would have been aged in used barrels. It's probably also barely straight, meaning two years and a day. Of course, any mixture of straights is a straight, but no other mixture gives you any real advantage. A mixture that is mostly straight corn lets you call something straight that's mostly aged in much cheaper used barrels. I know the brand's web site says it's aged in new, charred barrels but, of course, the bourbon component would have to be. And web site content isn't monitored by TTB.
Knowing the opportunistic nature of that company's business model, that would be a clever thing to do with some young bourbon and corn, both of which they could have gotten from Heaven Hill, but others as well. HH is the only major that makes and sells straight corn but other people make it for use in their blends, and blends are most of what Western Spirits/Three Springs makes in terms of whiskey. We also know HH makes straight (i.e., aged) corn, because their 'Mellow Corn' is a BIB.
Likely impossible to confirm, of course, but what do you think of the theory?