I have a Handy lift that was manufactured on the late 1990's, long before the sale of the company. So my Handy lift may not be apples to apples to your "post sale" Handy lift.
That said, I went out and looked at mine. The stroke of the cylinder controls the roller travel within the channel. With the cylinder fully retracted, the rollers are contained within the channel. With the cylinder fully extended, the rollers are contained within the channel. So...with the lift properly assembled and set up, it's not possible for the rollers to escape the channel.
I suppose it's possible there was a design change or a manufacturing error on your lift, but I doubt it. Since you noted your table was not level when retracted prior to your incident, I suspect it's more likely the rollers escaped from the channel at some point while being handled during the transport to or from your friends. If the lift was picked up high off the ground by the front of the table (it would have to be by fork lift or overhead crane or something similar), the roller could then escape the channel, even while still attached to the cylinder.
I'll predict Handy will say when their lift is correctly assembled and set up, what you describe cannot happen, and they'd be right. But with inadvertent handling of the lift, resulting in the roller exiting the channel while being lifted from the front of the table, what you describe and show in your photos can absolutely happen. So if there is a flaw in the design, the flaw is it is possible to set up and install the table incorrectly, resulting in your incident. But again, when set up and installed correctly, what happened to you isn't going to happen, because it's not mechanically possible. When set up and installed correctly, the cylinder stroke limits the travel of the rollers, and makes it impossible for the rollers to leave the channel at either end during normal table operation.
Hope that made sense... Very sorry your bike was damaged and very happy you were not injured..