So I had another thought based on how you described the action of the chain compared to another bike when backpedaling. If the freehub/freewheel on the back wheel is stiff, even a slightly mis-aligned chainring(front sprocket) or slightly bent tooth will make the chain jump off.
If you pull the rear wheel, the cogs there should spin in reverse pretty easily with a ratcheting sound. If it's stiff, the freehub (if it's that type) needs some work, and a very light grease. If it's a freewheel, I wouldn't take it apart, but soak it in penetrating oil to see if that helps.
This may be more a job for a bike shop, and it may not be worthwhile on a Huffy.
If you pull the rear wheel, the cogs there should spin in reverse pretty easily with a ratcheting sound. If it's stiff, the freehub (if it's that type) needs some work, and a very light grease. If it's a freewheel, I wouldn't take it apart, but soak it in penetrating oil to see if that helps.
This may be more a job for a bike shop, and it may not be worthwhile on a Huffy.