I got curious, and a bit of googling found this claim that
"In 1935, the Legislature transferred the portion of Camp Mabry east of the railroad track to the Highway Department, which had begun using part of the area for equipment maintenance as early the mid-1920s. Known as Camp Hubbard, named for former highway commissioner R.M. Hubbard, this area now is used by TxDOT for various purposes, most notably as the headquarters of the Vehicle Titles Division in the five-story Building # 1, built in 1955. "
https://txcompost.blogspot.com/2014/03/bull-creek-from-oakmont-heights.html
So presumably the "Camp" was inherited from when it was part of Camp Mabry?