I believe that the explanation is that this is a 1995 frame that features the flatter Top Tube with short Seat Tube Extension.
The Rhomboid of the front and rear triangle appear to show the Down Tube parallel with the Seat Stay along with a parallel Top Tube and Chain Stay. This is only possible with a 17” Hei Hei frame with the flatter Top Tube. If the frame were the more common Geometry of Slopping Top Tube with longer Seat Tube extension, then the Rhomboid would only be parallel with an 18” frame.
I will stand corrected if I saw the removed material from the Seat Tube, but I would say that everything else points to this being a 17” 1995 Hei Hei that has the Flatter Top Tube design and is fitted with replica Decals.
Pip