Part of the area they're citing as Hill Country is what we call Central Texas. Bell County borders Williamson County which is very much part of the Boom area.
Last week a couple of staff writers at the Austin American-Statesman asked in an op-ed piece, "Will Austin-San Antonio become the next DFW?" (Dallas-Fort Worth for those not in the know.) They made some compelling observations.
"22 percent of the half-million people who moved to Texas in 2015 landed in the San Antonio or Austin areas...