Ah, one of those age old questions often debated well into the night, like the existence of Sasquatch or whether Elvis is really dead? (I’d believe the former before the latter). Although Jack Daniel’s is actually distilled much like bourbon, according to old Jack it is definitely NOT bourbon and never wanted to be!
One difference is a sugar maple charcoal leaching process Daniel’s employs prior to barreling that isn’t generally used in say, Kentucky bourbons, but the real reason goes back to shortly after Prohibition when the original owners, the Motlow family, petitioned the US Treasury Dept to classify JD as a whiskey and not a bourbon – as the government originally required. After testing the Treasury Dept concurred and Jack Daniel’s has been designated as a whiskey ever since.
Cheers!