Well, if it was dredged up offshore, then it probably does come from the Yuan force; they've been finding a lot of interesting stuff from the invasion fleet. In which case it is far more likely to be "Chinese" than "Mongol".
I do wonder if this is an actual find or just a reconstruction, though. The only site on which I can find it -
http://www.maritimeasia.ws/topic/chronology.html with a link under the 1281 entry - doesn't say anything about it. And other sites on the Takashima finds mention only
fragments of red leather armour - see
http://www.archaeology.org/0301/etc/kamikaze.html for example. Could this just be a reconstruction from the fragments?
On the other hand they do seem to have found at least one fairly complete armour, the plate-lined one illustrated at
http://www.ualberta.ca/~chor/mongolin.htm so finding another complete armour is not impossible.