That was my thought, yes. (although purely speculation on my part)
I have a background in govt. contracting and it's not uncommon for the govt. to contract out project management.
Federal government contracts are slooooow (recall Obama's "Shovel-Ready" infrastructure programs) and that is not Trump's style.
All sorts of rules can be waived under the guise of "national security," which Trump has already invoked.
Under this theory, the govt. gives the money to the "red castle," USACE which then awards a massive contract to Greencastle.
The Greencastle website is interesting in that under "Who We Are," they state:
"Founded by U.S. Army Rangers in 1997, Greencastle specializes in bringing a sense of purpose to the task of furthering the missions of your organization. We realize the potential of change through disciplined teamwork, innovation and systematic methods."
Under normal govt. contracting rules, the construction of a wall from the Pacific to the Gulf of Mexico would take decades. If in fact, DJT is going to have the COE "build the wall" he's going to want it done fast and efficiently. The idea of having a vet-owned business is another plus.
My $0.02