We just bought a 2018 F-750 at work. for $120 ford takes takes the 33,000 GVW sticker off and slaps one on that says 25,999lbs to keep you out of CDL territory. So there is no telling how his truck is rated, i agree it should be sufficient though.
Never heard of that option before. Sounds strange. Also a loophole to escape excise taxes, that would likely close in the future.
edit:
In this case I believe "heavy" means over 55K GVW?,
https://www.ttnews.com/articles/senate-bill-would-repeal-federal-excise-tax-heavy-truck-sales