Sounds like a limit screw was a little off... rear wheel lock ups are not fun.
Had one a few weeks ago that was not chain related... the cone lock washer on my 3 speed sheared off on the non drive side and this frees up the bearing which then tightens itself and stopped the wheel. This happened at low speed and there was no lasting damage.
This was not anything I could fix on the road and had to walk a few miles back to the shop to install a new lock washer.