Thanks to some research, a few comments and an email from Jenny we solved the mystery of the package I purchased.
The package of Yerba Mate was right beside the Pan in the Mexican and South American food section. The label on the shelf was covered by a stack of food but the packages were peeking out over top.
See the resemblance?
What I thought was a bag of coarsely ground cornmeal (the package resembled the same type of packaging) turned out to be a kilogram of loose tea.
Um, we don't drink that much tea. Thankfully the kind cashier took pity on us (snickering all the while) and returned the package.
Wouldn't you have made the same mistake?