Better wander over to Dahon forums to see how to get the pin out. In many hinge designs the pin is held by a grub screw (or set screw) at the middle region. Remove the set screw and the pin should in theory be able to be extracted. There is a hole with screw thread cut into it at the pin's bottom end; put the bike upside down. Screw a machine screw into the hole which provides a gripping location to pull the pin out.

I predict you won't be able to get it out. The pin is stainless steel, while the frame is aluminium. Rain plus contaminants cause a galvanic reaction, forming aluminium oxide, which is larger in volume than bare aluminium. The result is the pin gets more and more constricted. For the same reason, aluminium quill stems and seat posts get stuck in steel frames.

I think your only hope is to thread in a looong rod with a nut near the opposite end, and a sleeve hammer around the rod to provide some very serious extraction hammering action.

You can also try some very penetrating thin oil dribbled in from the bottom and in between the hinge surfaces. Working the hinge to and fro may have the desired effect. I had limited success with this. I was unable to extract the pin.

I think this is a design flaw, or at least a manufacturing flaw.

[edit] I just thought of another way to force the pin out: With a precise thickness spacer with hole large enough for the pin to fit through, this may provide a surface to provide extraction force using the machine screw screwing into the pin. When the machine screw/bolt's head contacts the spacer, the pin will get forced out by progressive tightening of the bolt. With each bit of success, another washer may have to be inserted under the bolt head.