Was it defiantly a folder? Possibly a renovated and modified Moulton or Raleigh 20/RSW?
Tubing was round so not a Moulton. Not a tsr either. No I can't guarantee it folded. The bracket looked like it did, can't see any reason for bracket if not part of folding system.
I do think it had a hinge on the maintube.
Another idea was a mobiky, but tubing round and they tend to be silver. I do see the occasional mobikey, and the tubing is very low slung. Very Brompton like put I think it had straight top tube. Flat bars I think.