I actually kind of figured as much… But it could be attached in a more secure fashion, to perform double-duty? The suggestion of threading the chain through the seat rails seems possible, but I wonder how many chains will thread comfortably through… Anyhow, it was more of an open question than anything, really seems an elegant solution to locking up a folder…!
The point of the zip tie is to avoid double duty.
If you want double duty you can just attach it with the padlock, but then when you take off the padlock for locking the chain falls off and you have to hold it in place while simultaneously threading the other end through the wheels and such. So it's better to have two separate mechanisms: one for holding one end of the chain in place and another for actually locking.
Also the chain being threaded through the seat rails is the reason why it needs to be attached and, in fact, the whole point (to bring all the folding parts together and together lock them to a permanent fixture).