He apparently worked there at the county Health Department, so that at least leaves open the possibility that it was a workplace incident. It does seem like an unlikely target for terrorism, but of course he could have decided that it was simply a nice soft target that he knew well. And it’s also strange that he would recruit two others to go shoot his boss.
One thing that bothers me about searching for motives (exemplified by this comment) is that ultimately it doesn’t matter all that much whether he was a jihadist, a right-wing terrorist, someone who flipped out, or someone with violent mental illness. The final MO is the same - go with a large-magazine gun to a place with lots of people and shoot as many as you can. And they’re similar because we (by which I mean Republicans and the NRA) make it so easy to do.