And you are surprised by this?!
I've seen in several reputed museums some geographical alocations that would surprise you even more (like a wootz Indian Tulwar atributed to Libya or a Javanes Kris atributed to India).
So, don't give too much weight to the inscription and remember it was written by a person who may have had absolutely no knowledge about the item.
PS: And maybe Mr. Pinson bought it in a flea market in Zanzibar and concluded it must belong to the place.