It could just be that he knew it was a target rich environment. Country music fans run the gamut these days. A lot of it isn’t even “country music”. It’s more like “pop music”, one level above boy bands. .
It could also be that he gave more thought to his shooting perch. In the hotel, strategically overlooking the concert site. The fact that it was a country music concert may be a sad coincidence. Based on the limited knowledge we have at this point, we mustn’t exclude the element of random chance.