I agree that the only purpose served by the rod is to suspend the floor framing
However the bottom "chords" of the truss' are resolving most of the outward thrust of the roof (those collar ties are way up there)
The location of the floor beam down on the post below the plate means there is a lot of thrust on the post/beam conection
And it looks as tho some repair has been done with steel at the post plate conection.
Interesting...a little spooky...but interesting

I have the same arrangement in my 1905 barn, although the top of the truss is only waist high and spans 32' and runs parallel to the ridge line. Was originally a hayloft. There is no post down below on the main floor and is very stout.

Even though I am a little late with my two cents but here they are anyway.

This is nothing else but a king post truss were the "king post" is a metal rod thus allowing for a long clear span on the first floor with no obstructions like posts. It does nothing for the roof and does not need to. The rod is on tension with the floor practically hanging on it. The braces are on compression and transfer the load to the exterior walls near the post. The tie beam is therefore also under tension. They might have use a rod instead of a post because it is less intrusive. Reminds me of a german build roof systems.
So the only thing different compared to what one finds in most other barns is the fact that tha truss is seperated from the roof/rafter. Not so unusual after all.

I recently evaluated a barn in Pennsylvania which had multiple additions and modifications. One of the additions had a very similar "King Rod" arrangement, not attached to the roof system. It was obviously in place to allow the clear span below which happened to be open to the exterior as it was a dairy barn and the cows came in under this part of the addition. It was a bit unconventional from my limited experience, but it seemed a very logical and simple solution. If I can find a photo, I'll post it.