Second picture is a closeup of how the hitch mounts to the trailer. Never seen one like that. Looks like it was designed to be swapped or adjusted for height without too much trouble
The channel mount is common, but I've never seen one with 3 cross bolts, the standard is 2. Looks fabricated otherwise it is a simple matter to buy whatever size coupler you wanted...
Adjustable Couplers - Trailer Couplers - Trailer Parts On-Line Store | Nuera Transport
The frame definitely doesen't look heavy enough to be a 10k trailer, IMO.