It was probably just a 2-color printing process and the alignment is just a bit off. I checked my copy of that stamp, too, which also shows the red square a bit raised than what a "normal" copy would be:

You can "flyspeck" these stamps and often find minor "freaks" but unless they having missing colors or major shifts in printing, there is typically no premium value.
(In fact, if you take my scan, you'll notice a white mark in the top of the "5" of "15" or in the "C" of "Canada" that some may consider to be small printing anomalies, but hardly worth noting, as most collectors wouldn't categorize it as an EFO.)