Putting some batteries and a motor on a truck chassis with a ~70 mile range doesn't require a strong EV play.
Getting a 10 year vehicle contract for the USPS with 2wd, 4wd, ICE and EV options requires a strong government vehicle contracting play.
Oshkosh makes lots of vehicles for the military. And also a fair number of niche commercial trucks. They know how to do the requisition process, and they know how to assemble vehicles.
Grumman had the last 10 year vehicle contract for the USPS; also a big military contract vehicle supplier. Grumman built the LLV on a base of GM parts, and Oshkosh is building the NGDV on a base of Ford parts, but otherwise, pretty similar deal.