Is my meter faulty?

@desseardo How long did you give it before testing and at what intervals did you test afterwards?

It may have taken a while to show up.

Glycemic Index of Dark Chocolate
Dark chocolate has a GI of 23, according to the University of Sydney GI Database. These GI values fall in the very low glycemic index category, which means eating dark chocolate won't make your blood sugar levels peak, then crash a few hours later. Rather, dark chocolate -- chocolate with a cocoa content of 70 percent or higher -- will help you stabilize your blood sugar levels if eaten as part of a low glycemic index diet.

GI of milk chocolate is around 49. Still considered low GI but is worse than dark choc.