IIRC, that location is (barely) within the Fredericksburg city limits, so it would have been a city installation, not a VDOT installation. The independent cities are not fully beholden to VDOT when it comes to traffic control devices. For example, both Norfolk and Virginia Beach have been using red left arrows for over 10 years.
Adam, that's correct on all counts. In Northern Virginia, I have long observed that the incorporated cities and towns, which usually maintain everything within their limits save for some freeways and expressways, don't always comply with VDOT's way of doing things. Falls Church, Alexandria, (the City of) Fairfax, Vienna, Herndon and Leesburg all design their signals in ways that don't look like VDOT installations. Especially Alexandria
Even Arlington County, which maintains its secondary system (while VDOT maintains the numbered primary highways), seems to do some things in ways that do not always have the VDOT "look and feel."