I think they had no idea what they were, so they called them nickels. They may have been nickel sized.
Umm, those "nickels" are actually stuivers. (The Dutch coins they found were stuivers, half stuivers and double stuivers.) In Dutch, stuiver is a common term for the 5 cent coin - and the US English equivalent would be the nickel. Had the English article said "stuiver", some would probably have asked, huh, what the heck is that ... Christian
I find it much more likely that the blogger improperly translated "stuiver" as "nickel." He could easily have said "stuiver, a Dutch silver coin..."
Well Mat, those lil Dutch folks will be walking around a bit taller, with all that money in their little wooden shoes.