Looks fake to me.
Fleer used to stamp them like this 01/01 or 1/1.
this is true for later fleer product, their first #ed product I believe was the 96/97 Flair Showcase legacy collection, the numbering is ## of ##, and I've seen and own several cards (from year 2002 and prior) they have ## of ## numbering.
Back to the card in discussion: Looks fake to me. 1of1 card typically have different foil color, that card (unripped jersey from authentix) seems like normal card nothing stands out. And yes, the stamp does look odd.