Something “tasting” milchigs is a silly argument.
If the box has an OU (no D), and if you didn’t add dairy, and if there is no OU kosher alert on your item that the status may have changed from OU to OU-D, then your item is parve.
I went on the OU website, and Duncan Hines Family Style Brownies-Milk Chocolate is listed as Parve.