Yes they were milled out of a solid bar. I am no machinist at all either. I had a lot of help from machinist and other knife makers that showed me how to do it. I like it better than attaching bolsters by welding or soldering. It takes a little longer but works better for me in the end.
I made up a plate with a cleat on the back to hold in my vice and square all edges. I drilled some pin holes inline and drilled and tapped some holes for hold down clamps. I scribe where the bolsters will be, line it up with a machinist square and clamp it down. When I get to where the cap will be I loosen the clamps and lineup that scribe mark and finish milling to the line.
Here is a photo of what I use on my mill drill.
View attachment 31912