If this is true, then it would be a missing piece from von Scherling's collection. Prof. Klaas Worp and Renate Dekker have diligently been working to reconstruct von Scherling's collection over the years and this one may add to the fragmented picture. Of course there is no way to assess the authenticity of the description unless the seller is willing to talk about the fragment. However, I doubt a seller would know the name of von Scherling unless he saw it somewhere or new about the purchase, the owner, or both. Given that von Scherling's descriptions were usually accurate about language of composition and contents, it is my hunch that the card on the back was written by someone else, perhaps a non-specialist owner. There is a hand-written number on that card that reads "3106." I don't think this is a Rotulus number (von Scherling's private catalogue that buyers and potential buyers would consult), but it could possibly be one of the items sold outside Rotulus (these had different numbers). If it is a von Scherling item, I think it might be no. 1696, listed in the June 1933 issue of Rotulus and described as a "Coptic papyrus. Ten imperfect lines in Cursive uncial letters, part of a document or letter, verso blank (with transcription) (4:2.5 inches) 7th century (Egypt)." Everything is consistent with what we see on the eBay papyrus, except the dimensions listed on the card.
Update: I received the following private message from Prof. Klaas Worp (posted here with permission):
"Comparing the description of the piece given on eBay, I conclude that this item MUST be Rotulus 3 (1933) no. 1696. So, this fragment was already on the market in the year 1933 and might have been swimming 'up Rhine' from Leiden (the 'Old Rhine' river curves through part of the town!) to Basel or so already before the start of WW II."